Onion Tart

This tart is really more of a pizza, with a bready dough base and flat shape. It was amazing and pretty easy to make, although I found it a bit too heavily spiced. Next time I make it I will halve the seasonings and let the onions stand out on their own (don't cut down on the mustard though, it's delicious). The recipe below contains my adjustments.

Onion Tart with Mustard and Fennel
2 1/4 teaspoons active dry yeast (a 1/4-ounce package)
1/2 cup warm water (105 to 115°F)
1 1/2 to 1 3/4 cups all-purpose flour
1 large egg
2 tbsp plus 1 tablespoon extra-virgin olive oil, divided
1 1/2 teaspoons salt, divided
1 teaspoon fennel seeds
3 pound yellow onions, halved and thinly sliced
1 tablespoon Dijon mustard (I used a bit more)
1/2 cup grated Parmigiano-Reggiano

Stir together yeast and warm water in a small bowl and let stand until foamy, about 5 minutes. 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 teaspoon 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 2 tbsp 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 ½ teaspoon salt, and 1/4 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.

Knead dough gently on a floured surface with floured hands to deflate. Pat out dough on a large heavy baking sheet 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.