This tart, along with a cheese-custard filled one and a thin onion soup are the main element of the dawn breakfast eaten in Basel for the first day of Fasnacht, their annual Carnival celebration.  We would certainly think of it more as an appetizer or a brunch dish.  The secret of a good onion tart is cooking the onions for a long time to fully develop their sweetness.  The method below is geared toward first releasing, then evaporating the high water content of the onions, so that you are left with a vividly flavorful base for the tart filling.

Here’s a link for more information about Basel Fasnacht:  http://www.fasnachts-comite.ch/en/

One 10 or 11-inch tart, about 8 generous servings


Flaky Pastry Dough

1 1/2 cups all-purpose flour (spoon flour into dry-measure cup and level off)

1/2 teaspoon salt

1 teaspoon baking powder

10 tablespoons (1 1/4 sticks) unsalted butter, cold, cut into 12 pieces

1 large egg

1 large egg yolk

Onion Filling

1/2 cup (about 3 ounces) diced thick-cut bacon

3 tablespoons unsalted butter

2 pounds white onions

1 tablespoon all-purpose flour

1/2 cup milk

1/2 cup heavy whipping cream

Salt, freshly ground pepper, and freshly grated nutmeg

3 large eggs

One 10 or 11-inch tart pan with removable bottom

  1. For the dough, combine the flour, salt, and baking powder in the bowl of a food processor fitted with the metal blade.  Add the butter and pulse about 20 times to mix the butter in finely.
  2. Add the egg and yolk and pulse until the dough just begins to form a ball, but no longer.  Invert the dough to a floured surface and carefully remove the blade.  Use your hands to press the dough into a disk about 1/2-inch thick.
  3. Roll the dough and use it to line the tart pan, pressing it well against the bottom and sides of the pan before severing any excess dough at the rim of the pan.  Chill the crust while preparing the filling.
  4. Cook the bacon uncovered over medium heat in a large pan, such as an enameled iron Dutch oven, which will easily hold the onions later.  Stir occasionally so that the bacon colors evenly and remove it with a slotted spoon when it is crisp.  Drain the bacon on a plate coved with a paper towel.
  5. Pour off the bacon fat from the pan and add the butter.  Place the pan over medium heat, add the onions, salt them generously, and wait until the onions begin to sizzle.  Decrease the heat to low, cover the pan, and cook the onions for about 20 minutes, or until they have exuded a lot of water.  While they are cooking, uncover the pan occasionally and stir the onions.  Uncover the pan and let the onions continue to cook slowly until they are very reduced and golden.
  6. When the onions are almost cooked, set a rack in the lowest level of the oven and preheat to 350 degrees.
  7. Put the flour in a medium mixing bowl and whisk in the milk a little at a time.  After all the milk has been added, whisk in the cream.  Stir in the onions and taste for seasoning.  Add more salt if necessary, and grind in some pepper and a very little nutmeg – it should be slightly over seasoned to make up for the addition of the eggs.  Whisk in the eggs.
  8. Pour the filling into the tart crust and scatter the bacon over it.
  9. Bake the tart until the crust is baked through and well colored on the bottom and the filling is set and puffed, about 30 minutes.
  10. Cool the tart on a rack before unmolding.

Serving:  If you want to serve the tart as soon as it is baked, get everything ready early in the day or the day before so you’ll only have to scatter and pour everything into the crust before baking.  Just be careful not to get burnt before unmolding the tart from a hot pan.  This makes a great lunch with a green salad and a fruit dessert.

Storage:  Loosely cover the cooled tart with plastic wrap if you are going to serve it at room temperature.  Wrap and refrigerate leftovers and reheat them briefly at 375 degrees before serving.

Variations

Swiss Onion and Cheese Tart:  Add 3/4 cup (about 3 ounces) coarsely grated Gruyere, sprinkling the cheese on the filling after the bacon.