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Tarte á l’Oignon – French Onion Tart


For the Tart base

  • 1 stick cold unsalted butter
  • 1 cup unbleached all-purpose flour
  • ¼ teaspoon salt
  • 2 tablespoons cold water


  • 1 tablespoon olive oil
  • 2 tablespoons butter
  • 4-5 large onions thinly sliced
  • Salt to taste
  • 2 eggs whisked
  • 1/2 C gruyere
  • 3 Tbs whole milk
  • 2 Tbs crème fraîche

For Garnish

  • 3 thyme sprigs


Make pastry: Step1

  1. Blend together flour, butter and salt in a bowl with your fingertips or a pastry blender or pulse in a food processor.
  2. Mix until most of mixture resembles coarse meal with some small (roughly pea-size) butter chunks. Gradually add in ice water and gently stir with a fork (or pulse in processor) until incorporated.
  3. If the pastry holds together, it's ready. if it doesn't add a bit more water and work it in. Be sure to not overmix the dough.
  4. Gather dough together and flatten into a disk. Wrap in plastic wrap, chill until firm, at least 1 hour.

Step 2

  1. I made three smaller tarts out of the dough, but you can simply roll it out to cover a 9 or 10 inch tart pan.
  2. Roll out the disk of dough on a floured surface with a floured rolling pin into a round to fit into your tart pan. Trim excess dough, leaving a 1/2-inch overhang, then fold overhang over pastry and press against side to reinforce edge. Lightly prick bottom with a fork and chill until firm ( about 30 minutes)
  3. Partially blind bake the tart shells for about 10 minutes ( I had three small so it took lesser time) at 400*F. You may need more time for a bigger tart shell.

Tarte á l’Oignon

  1. Preheat the oven to 425ºF. In a heavy pot combine olive oil, butter, sliced onions and salt. Sautee the mixture until it starts to sizzle, then turn the heat down to a simmer, cover, and cook for 30 minutes, stirring occasionally until the onions are sweet and caramelized. Add in pepper to taste.
  2. Set aside to cool.
  3. Combine eggs, milk, creme fraiche with onions. Spread the onion mixture on top of the partially blind baked shells. Top with cheese and a sprig of thyme. Bake in the middle of the oven for 30 minutes or until the top is golden brown.
  4. Serve at room temperature.