Tart with French Onion Filling

Delightful French Onion Tart

Every time I dive into the world of savory tarts, I experiment with various crust combinations, all in search of that perfect blend. The following recipe draws inspiration from the classic Larousse Gastronomique. If you have a favorite crust that you cherish, don’t hesitate to use it! And remember, store-bought crusts are a perfectly valid shortcut if time is tight. I also find myself fluctuating on whether to pre-bake the crust — blind baking leads to a crisper, richer-colored shell (as long as you heed my timing suggestions!), but if you prefer convenience over crispness, feel free to skip this step; the filling can still be placed in an uncooked shell, albeit with a lighter color.

Ingredients

Crust

• 2 cups (250 grams) all-purpose flour
• 1/4 teaspoon table salt
• 1/2 cup (1 stick, 4 ounces or 113 grams) chilled butter, cubed
• 3 tablespoons cold water

Filling

• 1/2 pounds yellow onions (about 4 medium), halved and thinly sliced
• 1 tablespoons butter
• 1 tablespoon olive oil
• Just under 1/2 teaspoon table salt
• A pinch of sugar
• 1 cup low-sodium beef, veal, or mushroom stock/broth
• 2 teaspoons cognac, brandy, or vermouth (optional)
• Freshly ground black pepper to taste
• 1/2 cup (about 2 ounces or 60 grams) grated Gruyere, Comte, or Swiss cheese
• 1 large egg
• 1/2 cup heavy cream (half-and-half or milk may also work, but cream is preferred)

Creating the Crust

In a large bowl or food processor, combine flour and salt. Incorporate the chilled butter; you can either rub it into the flour with your fingers, use a pastry cutter, or pulse in a food processor until it resembles coarse breadcrumbs. Gradually add cold water, mixing until the dough forms into large clumps. Carefully knead it into a ball; it should feel firm yet still be easy to roll.

Lightly grease a 9-inch tart pan with a removable base. If you don’t have one, a regular pie dish or a 9-inch cake pan will do, though it may be tricky to unmold later. Roll out your dough between two sheets of plastic wrap until it’s approximately 11 inches in diameter. Remove the top layer of plastic, and gently transfer the dough into the tart pan, draping it to avoid stretching. Press it down into the corners and trim off the excess, leaving a slight overhang to account for shrinkage. Chill the crust in the freezer for 15 minutes.

If you decide to par-bake the crust, preheat the oven to 400°F (200°C). Lightly butter a piece of foil and press it into the chilled tart shell. Fill with pie weights, dried beans, or any available substitute, and blind bake for 12 to 14 minutes. Carefully take it out, remove the foil and weights, then return it to the oven for an additional 5 to 7 minutes until the edges are lightly golden. Set aside.

Preparing the Filling

In a large skillet over medium heat, melt the butter and olive oil together. Add the sliced onions, tossing them in the pan to coat with the butter and oil, then lower the heat to medium-low and cover. Cook for about 15 minutes, then uncover, stir in the salt and sugar, and sauté uncovered for another 10 to 15 minutes until they become beautifully caramelized and deep golden brown. If using, add cognac and the stock, cranking the heat up to scrape the pan for the delightful brown bits and simmer until the broth nearly evaporates, about 5 to 10 minutes. Adjust salt if necessary and season with freshly ground black pepper. Allow to cool until warm; you can expedite this by spreading the onions on a plate and chilling them briefly.

In a medium bowl, beat the egg and cream together. Gently incorporate the lukewarm onion mixture into this custard.

Assembling and Baking the Tart

Preheat your oven to 400°F (200°C). Pour the onion-egg custard into the prepared tart crust, filling it to 1/4-inch from the top. Should you need a bit more filling, whisk another egg with cream and add to reach that level. Sprinkle cheese over the mixture, and bake for 25 to 30 minutes, or until a knife inserted in the center comes out clean and no runny egg mixture clings to it. Enjoy warm or hot, ideally accompanied by a crisp green salad.