Swiss Onion Tart

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Preparation info

  • Makes one 10- or 11 inch 25- or 28 cm ) tart, about


    generous servings
    • Difficulty


Appears in

The Modern Baker

The Modern Baker

By Nick Malgieri

Published 2008

  • About

This onion tart, a cheese-custard filled tart, and a thin onion soup are the main elements of the breakfast eaten at dawn in Basel for the first day of Fastnacht, 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 here 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.


  • ½ cup (about 3 ounces/75 grams) diced thick cut bacon
  • 3 tablespoons unsalted butter
  • pounds (675 g) white onions
  • Salt
  • 1 tablespoon all-purpose flour
  • ½ cup milk
  • ½ cup heavy (whipping) cream
  • Freshly ground black pepper and freshly grated nutmeg
  • 3 large eggs
  • One 10 or 11 inch (25- or 28 cm) tart crust, unbaked, made from Rich Pie Dough, or No-Roll Flaky Dough


  1. Cook the bacon, uncovered, over medium heat in a large pan, such as an enameled cast-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 covered with a paper towel.
  2. 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 until they have exuded a lot of water, about 20 minutes. 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, another 20 minutes or so.
  3. When the onions are almost cooked, set a rack in the lowest level of the oven and preheat to 350° (180°C).
  4. 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 very little nutmeg—the filling should be slightly overseasoned to make up for the addition of the eggs. Whisk in the eggs.
  5. Pour the filling into the tart crust and scatter the drained bacon over it.
  6. 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.
  7. Cool the tart on a rack before unmolding.


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 very careful when unmolding the tart from a hot pan. This makes a great lunch with a green salad and a fruit dessert.


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°F (190°) before serving.


SWISS ONION & CHEESE TART: Add ¾ cup (about 3 ounces/75 grams) coarsely grated Gruyère, sprinkling the cheese over the crust before pouring in the custard.