Kalyn's Kitchen

Onion Gratin

This tasty Onion Gratin is flavored with rosemary and thyme, and it’s a perfect side dish for a special meal!

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Onion Gratin finished in baking dish

This Onion Gratin is a perfect Thanksgiving side dish and it’s also great for a special meal! 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, 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.

Onion Gratin process shots collage

How to Make Onion Gratin:

(Scroll down for complete recipe with nutritional information.)

  1. You can use any kind of onions, but cut the onions in thick half-inch slices after you peel them.
  2. 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.)
  3. While the onions roast, mix together mayo, lemon juice, Dijon mustard, grated low-fat pizza cheese, Pecorino Romano (or Parmesan) cheese, and pepper.
  4. Then spread the mayo-cheese mixture over, and bake until the topping is nicely browned.
  5. 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.
  6. Bake about 30 minutes or until nicely browned; then serve hot and wait for the compliments!

Onion Gratin square thumbnail of finished dish

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 finished in baking dish

Onion Gratin

Yield 6 servings
Prep Time 15 minutes
Cook Time 45 minutes
Total Time 1 hour

Onion Gratin is flavored with rosemary and thyme, and this is a perfect easy side dish for Thanksgiving or any special meal!


  • 6 medium-sized onions (see notes)
  • olive oil, for brushing onions
  • 1 tsp. finely minced fresh rosemary (see notes)
  • 2 T minced fresh thyme leaves (see notes)

Gratin Topping Ingredients:

  • 1/2 cup mayo
  • 1 T + 1 tsp. fresh-squeezed lemon juice
  • 3/4 tsp. Dijon mustard
  • 1 1/2 cups Pizza cheese blend (see notes)
  • 3 T grated Pecorino-Romano cheese (see notes)
  • 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 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.
  7. 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.)
  8. Place casserole dish in oven and bake about 30 minutes, or until top is golden brown and onions are slightly bubbling. Serve hot.


Use eight onions if your onions are small. You can use white, yellow, or Vidalia onions for this recipe. Use 1/2 tsp. dried rosemary, finely chopped with large knife if you don’t have fresh rosemary. use 1 T dried thyme, finely chopped with a knife if you don’t have fresh thyme. I used a cheese blend that had Mozzarella, Provolone, Parmesan, and Romano. Use grated Parmesan if you don't have Pecorino-Romano cheese.

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.

Nutrition Information:



Serving Size:


Amount Per Serving: Calories: 356Total Fat: 22gSaturated Fat: 5gTrans Fat: 0gUnsaturated Fat: 16gCholesterol: 20mgSodium: 512mgCarbohydrates: 31gFiber: 3gSugar: 7gProtein: 9g

Nutrition information is automatically calculated by the Recipe Plug-In I am using. I am not a nutritionist and cannot guarantee 100% accuracy, since many variables affect those calculations.

If you make this recipe I'd love to hear how it turns out. Leave a star rating or share on social media with the hashtag #KALYNSKITCHEN, thanks!

Low-Carb Diet / Low-Glycemic Diet / South Beach Diet Suggestions:
The gratin topping on this Onion Gratin with Rosemary and Thyme is more friendly for the original 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. Onions are really low on the glycemic index, so it would be approved for most other types of low-glycemic plans. Onions are relatively high in carbs, so this would be a splurge for low-carb diets.

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.

Pinterest image of Onion Gratin

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    60 Comments on “Onion Gratin”

  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!