This tart is a vehicle for caramelized onions. It’s also inspired by an appetizer I ate years ago in a Swiss auberge overlooking the Lake of Geneva, near our home at the time. It’s been so long, I don’t remember the name of the restaurant, but I do remember the onion tart. It was simple and rustic, just like the half-timbered dining room with its open fire where we tasted it. As we settled into our deep chairs and read the menu, our kir royales (champagne and creme de cassis) would arrive, accompanied by a complimentary sliver of tarte d’oignon. Sweet, rich and minimal, this tart was perfection in its simplicity. Today I make a version of this memory and enjoy another view from our California home. It’s so rich that I like to serve it a similar way, cut in thin slivers, served with a glass of wine.
Caramelized Onion Tart
For the dough – adapted from a recipe by Alice Waters:
1 cup all-purpose flour
1/2 teaspoon salt
6 tablespoons unsalted butter, chilled, cut in 1/4 inch cubes
3 tablespoons ice water
Stir flour and salt together with a fork. Toss in butter. Work the butter into the flour with a fork or your fingertips until it resembles coarse meal, with some pieces of the butter apparent. Sprinkle in the water while stirring with a fork until the dough comes together, adding another tablespoon of water if necessary. Form into a ball and flatten. Wrap in plastic wrap and refrigerate 1 hour
For the filling:
2 tablespoons olive oil
2 pounds yellow onion, peeled and thinly sliced
1 teaspoon salt
2 tablespoons port wine
1 teaspoon freshly ground black pepper
2 ounces finely grated Gruyère cheese
1 teaspoon fresh thyme, plus extra for garnish
1 egg, slightly beaten
Heat olive oil over medium heat in a deep skillet or pot. Add onions and salt. Cook onions, stirring occasionally, until they are golden brown, soft and squidgy, about 30 minutes. Add port wine and cook, stirring, 2 minutes. Remove onions from heat and stir in the pepper. Cool slightly.
While the onions are cooling, roll out the dough to fit in the bottom and up the side of a 10-inch round tart tin. Sprinkle half of the cheese over the bottom of the tart. Spoon onions into the shell and spread evenly. Sprinkle 1 teaspoon thyme over the onions. Brush the exposed crust rim with the egg wash. Sprinkle the tart and crust with the remaining cheese.
Bake in a preheated 375 F. oven until the crust is firm and golden and the onions have turned a rich golden brown, without blackening, about 30 minutes. Remove and cool slightly. Serve slightly warm or at room temperature garnished with thyme sprigs.