Roasted Tomato and Onion Frittata

By Ashley Lonsdale

Updated April 10, 2026

  • Christopher Testani for The New York Times. Food Stylist: Monica Pierini.
Media 1 of 1
Ready In
45 min
Rating
5(184)
Comments
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In the summer, tomatoes need little more than salt to reach near perfection, but roasting tomatoes any time of year alongside sweet onions concentrates their sugars and elicits a surprising amount of umami. This fragrant combination serves as the essence of this frittata. But the true hero of this recipe, if you can believe it, is a humble cup of full-fat Greek yogurt, divided between the frittata mixture and a simple sauce. The yogurt works to loosen the structure of the frittata, leaving the baked center eggy, delicate and tangy, with a little extra sharpness from Cheddar cheese, and also serves as a sauce, whisked with mustard and the savory juices left on the baking sheet to ensure no drop of flavor is forsaken. The consequence is a rich and satisfying meal that’s perfect for breakfast or lunch.

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Ingredients

Yield:4 to 6 servings

  • 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

Ingredient Substitution Guide

Preparation

  1. 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.

  2. 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.

  3. 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. 

  4. 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.   

  5. 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.)

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    Ratings

    5 out of 5
    184 user ratings
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    Comments

    LEW

    @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.

    Elizabeth

    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!

    Mimi Wu

    FWIW, you can really cut the prep time by doing Step 1 anytime and freezing it for later use. It’s a pro tip I learned from a dear friend and master baker: you can roast tomatoes, anytime, when they’re in season or not, for incredible flavor. They freeze beautifully.

    Gary

    I’m an onion and tomato lover and I enjoyed this recipe. I made it in a 12” cast iron skillet so I added two additional eggs, but the timings for both stovetop and oven worked just fine. After dividing the yoghurt mixture I did add some dried thyme, a grated garlic clove and a dash of chili flakes, and the sauce complimented the frittata beautifully.

    Noah

    Keep the oven at 425 the whole way through.

    Clare Cy

    Instead of using two pans, could you just use the sheet pan and cook the eggs in the oven that way? If you did, how would you modify the temperature and cooking time?

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