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Kalyn's Kitchen

Onion Gratin with Rosemary and Thyme

Onion Gratin with Rosemary and Thyme is a perfect side dish for a holiday meal, and it’s easy to cook, low-carb, low-glycemic, gluten-free, and vegetarian! Use Side Dishes to find more recipes like this one.

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Onion Gratin with Rosemary and Thyme found on KalynsKitchen.com

It’s time to start thinking about Carb-Conscious Thanksgiving Recipes, and this Onion Gratin with Rosemary and Thyme is a perfect Thanksgiving side dish and one that I’ve made over and over! I first came up this recipe when it rained for days and I had a ten pound sack of Vidalia onions to use up. I wanted something similar to the creamed onions my family always had for Thanksgiving, but I knew I’d have to get creative for a healthier onion dish, since the old family version had flour, butter, cream, and lots of full-fat cheese.What I ended up with was kind of a riff on the delicious Broccoli Gratin that’s also perfect for Thanksgiving.

You can use any kind of onions, but don’t skip the step of roasting them with rosemary and thyme before you assemble the gratin. When they’re in the gratin dish, the partly-cooked onions are spread with a topping made with mayo (or light mayo), lemon juice, Dijon, a blend of cheeses, and Pecorino-Romano (or Parmesan). Put that back into the oven to cook until the topping is starting to brown and you’ll have a winner.

When I first made this I was having my old house remodeled, and my contractors son loved it even though he told me, “I don’t like onions.” So I think a lot of people who aren’t normally onion fans might be won over by that cheesy topping.

And of course this is a perfect Meatless Monday dish, and it’s so good you might even make it the main course for a meatless meal, with something simple like Barely Blanched Broccoli Salad on the side! If you want more meatless recipes, follow my Meatless Monday Pinterest Board, which has ideas from Kalyn’s Kitchen and other blogs. I also have a great board for Best Low-Carb Meatless Recipes like this one; check it out!

Onion Gratin with Rosemary and Thyme found on KalynsKitchen.com

You can use any kind of onions, but cut the onions in thick half-inch slices after you peel them. I brushed the onions with olive oil, sprinkled them with fresh chopped rosemary and thyme, and roasted them for 15 minutes. (I used fresh herbs since I still have them growing, but finely chopped dried herbs will be just fine in this.)

Onion Gratin with Rosemary and Thyme found on KalynsKitchen.com

While the onions roast, mix together mayo, lemon juice, Dijon mustard, grated low-fat pizza cheese, Pecorino Romano (or parmesan) cheese, and pepper. Then spread the mayo-cheese mixture over, and bake until the topping is nicely browned. I baked it in a flatter dish this time, so I increased the amount of the topping to be sure it would cover all the onions. I’ll give you both those measurements in the improved recipe!

Onion Gratin with Rosemary and Parmesan found on KalynsKitchen.com

Bake about 30-40 minutes, then serve hot and wait for the compliments!

More Tasty Side Dishes for the Holidays:

Marinated and Roasted Vidalia Onions Rings with Parmesan from Kalyn’s Kitchen
French Potato Gratin ~ That Skinny Chick Can Bake
Sweet Potato Gratin with Goat Cheese, Parmesan, and Thyme ~ Kalyn’s Kitchen

Onion Gratin with Rosemary and Thyme

Onion Gratin with Rosemary and Thyme is a perfect side dish for Thanksgiving, and it’s easy to cook!


  • 8 small or 6 medium-sized white, yellow, or Vidalia onions
  • olive oil, for brushing onions
  • 1 tsp. finely minced fresh rosemary (or use 1/2 tsp. dried rosemary, finely chopped with large knife if you don’t have powdered rosemary)
  • 2 T minced fresh thyme leaves (or use 1 T dried thyme, finely chopped with a knife if you don’t have ground thyme)

Gratin Topping Ingredients (smaller amount for a deep square baking dish):

  • 6 T mayo
  • 1 T fresh squeezed lemon juice
  • 1/2 tsp. Dijon mustard
  • 1 cup Pizza cheese blend (I used a blend that had Mozzarella, Provolone, Parmesan, and Romano
  • 3 T grated Pecorino-Romano cheese (or use grated parmesan)
  • fresh ground black pepper to taste

Gratin Topping Ingredients (larger amount for a flat 9″ x 12″ baking dish):

  • 1/2 cup mayo
  • 1 T + 1 tsp. fresh-squeezed lemon juice
  • 3/4 tsp. Dijon mustard
  • 1 1/2 cups Pizza cheese blend (I used a blend that had Mozzarella, Provolone, Parmesan, and Romano
  • 3 T grated Pecorino-Romano cheese (or use grated parmesan)
  • fresh ground black pepper to taste


  1. Preheat oven to 450F/230C.
  2. Peel onions and cut in 1/2 inch slices. Spray or brush baking sheet with olive oil or non-stick spray, then arrange onion slices in a single layer. Spray or brush onions with oil, then sprinkle with fresh or dried chopped herbs.
  3. Roast onions 15 minutes, then take them out and turn oven down to 375F/190C.
  4. While onions roast, combine mayo, lemon juice, Dijon mustard, pizza cheese, Pecorino-Romano cheese, and black pepper in a small bowl. Mix together with a fork. (The mixture will be lumpy.)
  5. Spray a square 8″ x 10″ baking dish or a rectangular or oval 9″ x 13″ casserole dish with olive oil or nonstick spray.
  6. Remove baking sheet from the oven and use a turner to layer onions in the casserole dish. Spread topping over onions (I used a rubber scraper to spread it around. Don’t worry if the mixture doesn’t cover every bit of the onions.)
  7. Place casserole dish in oven and bake 30-40 minutes, or until top is golden brown and onions are slightly bubbling. Serve hot.


I’m guessing this would keep for at least a day in the refrigerator, but even though I have made this quite a few times, I’ve never had any leftovers!

This recipe was inspired by Onion Gratin at Closet Cooking and many creamed onion casseroles from my childhood

All images and text ©

Onion Gratin with Rosemary and Thyme found on KalynsKitchen.com

Low-Carb Diet / Low-Glycemic Diet / South Beach Diet Suggestions:
The gratin topping on this Onion Gratin with Rosemary and Thyme is more South Beach Diet friendly than the creamed onions of my childhood but this isn’t a low-fat dish, so this should probably be a “once in a while treat” for South Beach Dieters. It would be approved for most other types of low-glycemic or low-carb eating plans, although onions do have some carb so use portion control if you’re strictly counting carbs.

Find More Recipes Like This One:
Use the Recipes by Diet Type photo index pages to find more recipes suitable for a specific eating plan. You might also like to Follow Kalyn’s Kitchen on Pinterest to see all the good recipes I’m sharing there.

Nutritional Information?
If you want nutritional information for a recipe, I recommend entering the recipe into this nutrition analyzer, which will calculate it for you. Or if you’re a member of Yummly, you can use the Yum button on my site to save the recipe and see the nutritional information there.

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    60 Comments on “Onion Gratin with Rosemary and Thyme”

  1. When I use the recommended nutritional analysis site to calculate the macros, your recipes often come out fairly high in carbs. This one came to 24g per serve! Sounds high even for a carb-conscious recipe. Looks delicious though. 🙂

    • I just checked in Yummly and this recipe says 18 carbs there. Which is not super low, but onions do have some carbs. This illustrates perfectly one of the reasons I don’t want to calculate the nutritional information; it’s very hard to be accurate with people using different ingredients and eating different amounts. However, I will remove low-carb and Keto tags from this recipe; thanks for telling me.

  2. Pingback: Cauliflower Gratin - melissassouthernstylekitchen.com

  3. I am not a mayonnaise fan but in this dish, all the flavors blend really well together and it is delicious! I’m making it again for dinner tonight. I left out the herbs and used plain mozzarella instead of the pizza blend and my husband and I loved it. Thanks for a great recipe!

  4. Late to find this since comments are starting 2009! Sounds like a great way to onions – they are so good for you.

    I am not a mayo/miracle whip fan. Would crème fraîche work as a substitute? I saw it used in a broccoli gratin recipe.

    • Hi Michelle,
      I’m not actually sure how that would work as a replacement for mayo. I worry it might separate or get watery. Sorry, but if you try it I’d love to hear how it works!

    • Hi Michelle – I was thinking the same thing but then read her comment about separation. I’m thinking I’ll try it first by doing 1/2 mayo and 1/2 sour cream.  If that works then that might be my favorite but then I might try again with all sour cream.  I can’t imagine that it would separate as I’ve used sour cream in lots of recipes, sometimes by itself, sometimes combined with cream of mushroom soup and it has always been stellar so I’m going to give it a try.  I say to all my family and friends that when they come here to eat they should be prepared to eat in the “test kitchen”.  They love it!

  5. Looks and sounds yumm!!! I love onions so any recipe with onion is a big win for me! Gonna try IT

  6. I never used to think of onions as the main ingredient in a dish until you first posted this recipe. Thanks for bringing it back!

  7. This dish was one of the surprise hits at the Thanksgiving table today, delicious! Used vidalias and fresh herbs. I grew up with creamed pearl onions at holidays and this is a nice modern twist on that idea. Thanks!

  8. You could try sour cream, but I don't think it will be quite the same.

  9. It looks so yummy but I don't eat mayo…any other recommendations? Thanks.

  10. Wonderul dish! I made this last night to have with some grilled pork chops. In fact, I regularly make a recipe, I believe came from Southern Living originally, I salt & pepper my boneless pork chop, top with a nice slice or onion on top, add a heaping TBSP of mayo and cover with grated parmesan & bake at 375 for about 30-40 minutes. This will be a regular side dish at our house now!! Thanks!

  11. Eileen, I love onions (and mayo, but that's a different story.) This kind of gratin with just a little mayo is really flavorful.

  12. Wow, I really was not expecting to see a mayo-based cream! Super interesting. I am all about onions, and this sounds like a great way to eat as many as possible! 🙂

  13. Cee Jay, so glad you liked it!

  14. All I can say is "HIT"! And, I have more left over for lunch tomorrow!