Onion Tart with Mustard & Fennel

2 1/4 t. active dry yeast (a 1/4 oz package)
1/2 c. warm water (105-115 deg)
1 1/2-1 3/4c. all-purpose flour
1 large egg
1/3 c. + 1 T. extra-virgin olive oil, divided
2 1/2 t. salt, divided
2 t. fennel seeds
3 lb. yellow onions, halved and thinly sliced
1 T. Dijon
1/2 c. 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 c. flour in a medium bowl, then make a well in center of flour and add yeast mixture to well. Stir together egg, 1 T. oil and 1 1/2 t. 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 c.) 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 c. oil in a 12" heavy skillet over medium-high heat until it shimmers, then saute fennel seeds until a shade darker, about 30 sec. Stir in onions, remaining 1 t. salt and 1/2 t. 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 deg. F with rack in the 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 x 12" rectangle, turning up or crimping edge, then brush mustard evenly over dough,, leaving a 1/2" border around edge. Spread onions evenly over mustard, then sprinkle evenly with cheese.

Bake tart until crust is golden brown, 30-35 minutes. Cut into 2" squares or diamonds & warm or at room temperature.

Note: Onions can be made up to 2 days ahead and chilled, covered.

O.K. This one was well received. There were a few alterations and short cuts involved. I used Trader Joe's Pizza Dough in place of making my own crust. There were just too many other thing to do and yeast is just too unreliable for me in a trial run. If it is the only thing I am making, I'll give the dough a try with a pack of pizza dough in the fridge on stand by. The many comments online recommended more mustard and 15 x 12" seems like a lot of territory for a little ole tablespoon of mustard. So I spread it as thin as I could by back of spoon but enough that it made a definitely layer. I used easily 3-4 soup spoons of mustard. There were more than enough onions and I probably used extra cheese as well.