Roasted Tomato and Onion Frittata
Updated February 24, 2026
- Ready In
- 45 min
- Rating
- Comments
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Ingredients
1 ½ pounds tomatoes, sliced ¼-inch thick
1 medium sweet onion, halved and thinly sliced
5 tablespoons extra-virgin olive oil, divided
Kosher salt (such as Diamond Crystal) and freshly ground black pepper
1 cup plain whole-milk Greek yogurt
1 tablespoon Dijon mustard
6 large eggs
½ cup shredded sharp Cheddar
1 teaspoon chopped fresh thyme, plus more for garnish
Nutritional analysis per serving (4 to 6 servings)
11 grams carbs; 195 milligrams cholesterol; 264 calories; 10 grams monosaturated fat; 2 grams polyunsaturated fat; 5 grams saturated fat; 20 grams fat; 2 grams fiber; 660 milligrams sodium; 12 grams protein; 8 grams sugar
Note: The information shown is Edamam’s estimate based on available ingredients and preparation. It should not be considered a substitute for a professional nutritionist’s advice.
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Preparation
- Step 1
Heat oven to 400 degrees. On a rimmed baking sheet, toss tomatoes, onions and 3 tablespoons olive oil; season with salt and pepper. Bake for 17 to 20 minutes, until some onion edges are golden and the tomatoes have lost some moisture.
- Step 2
Meanwhile, in a large bowl, whisk together the yogurt and mustard; transfer ½ cup to a small bowl. In the same large bowl, whisk in the eggs, cheese, thyme and ½ teaspoon salt.
- Step 3
Heat a medium (ideally 10-inch) cast-iron skillet over medium-high and add the remaining 2 tablespoons olive oil. Add the egg mixture and cook for about 2 minutes, swirling to evenly distribute if needed, until the bottom is just set. While the egg mixture sets, arrange the tomatoes and onions on top in an even layer, using a metal slotted spatula and a great amount of care. Transfer to the oven and bake for about 10 minutes, until the frittata is just set.
- Step 4
Whisk 1 to 2 tablespoons of the tomato and onion juices from the sheet pan into the small bowl with the reserved yogurt sauce. Season to taste with salt and pepper.
- Step 5
To serve, divide the warm slices of frittata among plates and spoon a little yogurt sauce on top. Finish with a few cranks of black pepper. The frittata is best served warm, with the cool sauce for maximum contrast. (If making ahead, you can cool the frittata completely, slice and store in an airtight container in the refrigerator for up to 4 days. Store the yogurt sauce in a separate airtight container, topping reheated slices as desired.)
Private Notes
Comments
@Bruce A great quiche tip from the old Moosewood Cookbook, before pouring the egg custard into the shell, sprinkle the cheese in first. The cheese melts and forms a layer between the custard and the crust, helping to prevent the crust from getting soggy. Follow the par baking instructions for whatever crust you choose, then sprinkle the shredded cheddar evenly over the bottom, then pour in the egg mixture.
Took me much longer than 20 minutes to get to desired result with tomatoes, and the quantity of the tomatoes seemed very large in relation to the eggs. Mine did not look like the picture but was tasty!
@Arrested development Step 2 is the making of the sauce from the yoghurt and mustard. As outlined 1/2 cup of this sauce is saved for serving. The rest is used to make the frittata.
Delicious, but a few tweaks needed. There was too much oil in the cast iron skillet, my eggs were swimming. And because the tomatoes weren't ready in 20 minutes, the eggs sat in the hot skillet (off the burner, but cast iron retains heat) longer than I intended. Next time I'll make sure the tomatoes are done before starting to cook the eggs. I also had extra tomatoes, but they were a tasty snack later.
As someone else mentioned, the ratio of tomatoes seems off. I ended up using about a third less than the amount listed in the recipe. If I had used the entire amount requested, it would have required multiple layering of tomatoes and likely resulted in a watery finished product since the tomatoes still give off some moisture during the final cook. Overall, the taste of the finished frittata was good, but this will not be on my NYT's repeat list.
Fantastic and simple! Made this for dinner tonight, with avocado, salad and corn bread. We loved it and I'm sure will love it again tomorrow. We used and LOVED all the tomatoes, cooked for much longer than recommended (maybe 40 minutes) but wish I made a full cup of the sauce, we ate it all tonight and won't have any for the leftovers.