Onion Tart with Mustard & Fennel

Last updated on April 11th, 2012

“CLICK…CHOMP.” These were the sounds I made yesterday, while photographing one spectacular onion tart. Who can blame me for eating while working? The onions, which came from my garden, were sweetly-caramelized, and fragrantly-infused with fennel. Even the crust was delightful, for it had just the right amount of crunch. You can make this bit of poetry, too:

To make life easier, you can caramelize the onions a day or two in advance. You can even prepare the crust a day in advance. I let the slicing attachment of my food processor do the onion-slicing.

Onion Tart with Mustard and Fennel

Adapted from Gourmet Magazine

2 1/4 teaspoons active dry yeast (a 1/4-ounce package)

1/2 cup warm water (105-115°F)

1 1/2 to 1 3/4 cups all-purpose flour

1 large egg

1/3 cup plus 1 tablespoon extra-virgin olive oil, divided

2 1/2 teaspoons salt, divided

2 teaspoons fennel seeds

3 pound yellow onions, halved and thinly sliced

1 tablespoon [or more] Dijon mustard

1/2 cup grated Parmigiano-Reggiano

Stir together yeast and warm water in a small bowl and let stand until foamy, about 5 minutes. (If mixture doesn’t foam, start over with new yeast.)

Put 1 1/2 cups flour in a medium bowl, then make a well in center of flour and add yeast mixture to well. Stir together egg, 1 tablespoon oil, and 1 1/2 teaspoons salt with a fork. Add egg mixture to yeast mixture and mix with a wooden spoon or your fingertips, gradually incorporating flour, until a soft dough forms. Transfer dough to a floured surface and knead, working in additional flour (up to 1/4 cup) as necessary, until smooth and elastic, about 5 minutes. Transfer dough to an oiled bowl and turn to coat. Cover with plastic wrap and let rise in a draft-free place at warm room temperature until doubled, 1 to 1 1/2 hours.

While dough rises, heat remaining 1/3 cup oil in a 12-inch heavy skillet over medium-high heat until it shimmers, then sauté fennel seeds until a shade darker, about 30 seconds. Stir in onions, remaining teaspoon salt, and 1/2 teaspoon pepper, then reduce heat to medium-low and cover onions directly with a round of parchment paper. Cook, stirring occasionally, until onions are very tender and golden brown, 1 to 1 1/4 hours.

Preheat oven to 375°F with rack in middle.

Knead dough gently on a floured surface with floured hands to deflate. Pat out dough on a large heavy baking sheet (preferably blue steel) into a 15- by 12-inch rectangle, turning up or crimping edge, then brush mustard evenly over dough, leaving a 1/2-inch border around edge. Spread onions evenly over mustard, then sprinkle evenly with cheese.

Bake tart until crust is golden brown, 30 to 35 minutes. Cut into 2-inch squares or diamonds and serve warm or at room temperature.

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