French Onion Tart
French Onion Tart
A savory French onion tart with a crisp butter crust, deeply caramelized onions, a light cream custard, and nutty Gruyere baked until golden.
This French onion tart turns the best parts of French onion soup into a sliceable savory tart: slow-softened onions, a little mushroom stock for depth, a restrained custard, and a cap of Gruyere that browns at the edges. It is rich enough for dinner but tidy enough for brunch, especially with a sharp green salad on the side.
The filling depends on patient onion cooking. Covering the onions first helps them collapse without scorching, then the lid comes off so their moisture can cook away and their sweetness can concentrate. A splash of stock is reduced into the onions so the tart tastes savory and rounded rather than simply sweet.
A par-baked butter crust gives the cleanest slices and keeps the bottom crisp under the onion custard. The filling is intentionally shallow, closer to a tart than a tall quiche, so one egg and a little cream are enough to bind the onions without muting their flavor.
Serve the tart warm, not straight from the oven, so the custard has a few minutes to settle. Leftovers reheat well in a moderate oven, where the crust can crisp again and the cheese regains its browned, nutty edge.
Nutrition (per serving)
Directions
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1
Mix the flour with 1/4 teaspoon of the salt in a large bowl. Cut in the chilled cubed butter until the mixture looks like coarse crumbs with a few pea-size pieces.
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2
Sprinkle in the cold water and stir just until large clumps form. Press the dough into a disk, roll it into an 11-inch round, and fit it into a lightly buttered 9-inch tart pan.
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3
Trim the edges, prick the base lightly, and freeze the tart shell for 15 minutes while heating the oven to 400°F.
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4
Line the chilled shell with buttered foil and pie weights. Bake for 13 minutes, remove the foil and weights, then bake 6 minutes more, until the edges are lightly golden.
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5
Melt 1 tablespoon butter with the olive oil in a wide skillet over medium heat. Add the onions, cover, reduce the heat to medium-low, and cook for 15 minutes, stirring once or twice.
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6
Uncover the skillet, stir in the remaining 1/2 teaspoon salt and the sugar, and cook for 15 to 20 minutes more, until the onions are soft, golden, and lightly caramelized.
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7
Add the brandy, if using, and the stock. Raise the heat and simmer, scraping the browned bits from the skillet, until the liquid has nearly disappeared. Season with black pepper and cool until warm.
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8
Whisk the egg and cream in a medium bowl, then stir in the warm onions. Pour the mixture into the par-baked shell and spread it evenly.
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9
Sprinkle the Gruyere over the top and bake at 400°F for 25 to 30 minutes, until the custard is set and the cheese is browned in spots.
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10
Let the tart rest for 10 minutes before slicing. Serve warm or at room temperature with a crisp green salad.
Ingredients
- All-Purpose Flour:2 cups
- Table Salt:3/4 tsp
- Unsalted Butter, chilled and cubed:1/2 cup
- Cold Water:3 tbsp
- Yellow Onions, halved and thinly sliced:1 1/2 lb
- Unsalted Butter:1 tbsp
- Olive Oil:1 tbsp
- Granulated Sugar:1 pinch
- Low-Sodium Mushroom Stock:1 cup
- Brandy or Dry Vermouth:2 tsp
- Black Pepper, freshly ground:to taste
- Gruyere Cheese, grated:1/2 cup
- Large Egg:1
- Heavy Cream:1/2 cup
Tips & Notes
- If the onions start browning before they soften, lower the heat and add a spoonful of water.
- Mushroom stock keeps the tart vegetarian while still giving the onions a savory base.
- A store-bought 9-inch savory pie shell can be used when time is short; par-bake it according to the package directions.
- Cool the onions before mixing them with the egg so the custard stays smooth.
