Our favorite way to break in a new Field Skillet is to cook up a big batch of caramelized onions, which is both an excellent recipe for building up durable seasoning and it leaves you with a utilitarian ingredient that you can use to top burgers, sandwiches, and pizza, or as a flavorful base for soups and braises.

Here, we top a skillet-baked shell with Gruyère cheese and the aforementioned onions to make a tart that has all the deep flavors of a classic French onion soup.

Photo: Lauren V. Allen

Recipe: Caramelized Onion Skillet Tart

Yield: 4 to 6 servings



Make the tart crust: In a food processor, combine the flour, sugar, and salt and pulse a few times. Add the butter and pulse several times, until the mixture resembles coarse crumbs. In a small bowl, beat together the egg and water, then drizzle over the flour mixture and pulse a few times. The mixture should resemble a moist, coarse meal that holds together when you pinch it between your fingers. If it doesn’t, add another teaspoon of water and pulse again.


Dump the dough out onto a work surface, then smash and push it together until it forms a ball. Flatten the ball into a disk, then wrap in plastic and refrigerate for at least 3 hours, and up to 3 days.


Make the carmelized onions: Heat the oil and butter in a No.8 (or larger) Field Skillet over medium heat until the butter has melted. Add the onions, thyme, and salt and cook, stirring occasionally, until the onions begin to brown around the edges, about 20 minutes. Add the vinegar and a splash of water and continue cooking, stirring occasionally, until the onions are deeply browned and very soft, about 20 minutes longer. Transfer to a bowl and clean the skillet.


Blind bake the tart crust: At least 2 hours before you’re ready to eat, roll the dough out between two sheets of parchment paper until it’s about 12 inches in diameter. Transfer the dough to a No.8 Field Skillet and press it into the pan; the dough should reach about an inch up the side of the skillet. Fold the edges of the dough over to leave an even crust that’s at least ½ inch up the side of the skillet. Prick the base of the crust all over with a fork. Refrigerate the dough for at least 1 hour.


Meanwhile, preheat the oven to 400°F. Grease a piece of aluminum foil with butter or cooking spray and gently press it, greased side down, over the dough (make sure to cover the sides of the dough as well). Bake for 20 minutes, then remove the foil and continue baking until the tart shell is golden brown, about 10 minutes longer.


Scatter the cheese evenly over the bottom of the tart, and top with an even layer of the caramelized onions. Bake for 10 minutes longer, or until the cheese has melted. Let the tart cool in the pan for at least 20 minutes (it’ll shrink slightly during this time), then cut into wedges and serve.

Seasoning Rating: Best

When breaking in a new skillet, a big batch of caramelized onions will help develop seasoning across the entire cooking surface: butter, oil, and the natural oils released by onions as they cook will coat your skillet evenly throughout a 20-30 minute (or longer!) cooking session. Clean up promptly, using a Natural Fiber Brush to remove any small bits of fond stuck to the pan.

A single note of caution: it's fine to slice and serve the tart from your skillet, but it's best to remove baked goods from the pan promptly. Extended storage, especially in the fridge, can trap moisture against the cooking surface and side walls—conditions that can strip seasoning and promote surface rust.

Seasoning Ratings:

Best—These dishes are the best options for building resilient seasoning, and surefire choices for getting tricky pans back on track.

Better—The best way to keep your skillet in great shape is to cook frequently, and cast iron-friendly dishes like these are your bread and butter.

Safe—These recipes won't strip seasoning away from your pan, but won't really add any, either.

OK—Be sure to clean up promptly. Recipes with this rating might feature acidic ingredients which can affect seasoning if not washed soon after cooking.