Name: French Onion Tart
Prep time: 30 min
Cook time: 105 min
Total time: 135 min
Yield: 8 Servings
Ingredients: For the Cornmeal Crust; 1¼ cups all-purpose flour; ½ cup fine yellow cornmeal; ½ teaspoon kosher salt; ½ teaspoon cracked black pepper; ½ cup unsalted butter, cold, diced; 1 tablespoon fresh thyme leaves; 4 to 5 tablespoons ice water; 2 tablespoons olive oil; 2 tablespoons unsalted butter; 2 pounds sweet yellow onions, peeled, halved and thinly sliced along the grain; 1 teaspoon kosher salt; ½ cup apple cider; 1 tablespoon finely chopped fresh sage; ¾ cup finely grated parmesan; ¼ cup sour cream; Freshly ground black pepper; 1 teaspoon dijon mustard; 2 tablespoons unsalted butter; 8 to 10 fresh sage leaves

Mains

French Onion Tart

Author: Mary DiSomma

There’s nothing better than caramelized onions. The same slow cooking process that causes the Maillard reaction makes the onions jammy and sweet. Caramelized onions make an incredible addition to savory dishes like this French onion tart on a cornmeal crust. Thyme leaves and freshly ground black pepper add some lovely warm and herbaceous flavors, making this one of my favorites for fall entertaining.

This onion tart recipe takes some inspiration from Alsatian tarts (the real French onion tart!) but there are some key differences. Classic Alsatian tart recipes typically use puff pastry or pâte brisée for the crust. I think the cornmeal in this recipe really complements the caramelized onions, but feel free to experiment with different crusts after you’re familiar with it. If you’re interested in trying your hand at a more traditional Alsatian onion tart, check out my tips for working with puff pastry dough!

Ingredient Tips

A standard Spanish onion will make the best onion tart—yep, Spanish onions are different from other yellow onions. Spanish onions, yellow onions, and Vidalia onions each have their own unique flavor, texture, sugar content, and moisture level. A Spanish onion is its own unique variety that is mild in flavor, sweeter than a standard yellow onion, and very juicy compared to other varieties.

Aside from the signage at the store, you can identify a Spanish onion by its shape, size, texture, and color. Spanish onions are usually larger and rounder than standard yellow onions—comparable to a softball. They also tend to have lighter skins with a finer grain than regular yellow onions do. And finally, check the texture: Spanish onions are softer due to higher moisture content, so they should give slightly when you squeeze them.

If you can’t find a Spanish onion, Walla Walla and Vidalia onions both make good substitutes. A Vidalia onion tart actually sounds kind of good! Even a white onion can work in a pinch, but you might need to add a little sprinkle of sugar to help it along. And I do mean a little sprinkle—it only takes ½ to 1 teaspoon per pound of onion to kickstart the caramelization process.

Preparation & Preservation Tips

Poking holes in your pie crust helps it hold its shape during blind baking. This technique is called docking. Using pie weights when you parbake helps with this too. If you choose to skip either step, it’s more likely that your crust will bubble, warp, or crack.

Baking the pastry blind before adding the filling helps prevent the crust from becoming soggy. The layer of dijon also helps by creating a thin barrier between the onions and the pastry. Make sure not to skip the step where you squeeze excess moisture out of the filling mixture!

I like to make mine in a heavy Dutch oven or stainless-steel skillet. These pans allow moisture to evaporate evenly and help the onions brown beautifully. The trick? Don’t rush the process. Caramelization takes time. Stirring often prevents sticking and ensures every strand of onion gets that golden-brown finish.

Extra Tips

This tart makes a wonderful addition to an appetizer spread. Try placing it out alongside your other favorite apps, or pair it with a fresh salad before your main course begins. It would also fit in well at a brunch with friends! For an herbaceous brunch companion, try it with my Grapefruit and Rosemary Mimosa. Yum!