-
1
Stir together water, yeast, and sugar in a small bowl until sugar is dissolved, then let stand until foamy, about 5 minutes.
-
2
(If mixture doesn't foam, discard and start over with new yeast.)
-
3
Stir together 2 1/2 cups flour and 1 1/2 teaspoons salt in a large bowl, then add yeast mixture and 2 tablespoons oil and stir until a dough forms.
-
4
Turn out dough onto a floured surface and knead, adding enough of remaining cup flour, a little at a time, as needed to prevent stickiness, until smooth and elastic, about 8 minutes.
-
5
Form dough into a ball and transfer to an oiled large bowl, turning to coat with oil.
-
6
Cover bowl with plastic wrap and let dough rise in a draft-free place at warm room temperature until doubled in bulk, about 2 hours.
-
7
Cook onions in remaining tablespoon oil with remaining teaspoon salt in an 8- to 9-inch nonstick skillet over moderately low heat, stirring, until slightly softened, about 2 minutes.
-
8
Cover surface of onions with a round of parchment or wax paper (or cover skillet with a tight-fitting lid) and cook onions, lifting parchment to stir frequently, until very soft and pale golden, 12 to 15 minutes.
-
9
Transfer dough to a 15- by 10- by 1-inch baking pan and stretch dough, first by pulling with your hands, then by pressing your fingertips into dough and working outward from center, until dough fills pan.
-
10
Prick dough all over at 1-inch intervals with a fork, leaving a 1-inch border all around sides, and cover loosely with oiled plastic wrap (oiled side down).
-
11
Let dough rise slightly in draft-free place at warm room temperature, 30 minutes.
-
12
While dough rises, put oven rack in middle position and preheat oven to 400F.
-
13
Gently brush dough with some egg wash, being careful not to deflate dough.
-
14
Scatter onions evenly over dough, leaving a 1-inch border, then sprinkle with nigella seeds.
-
15
Bake until top is golden and bottom sounds hollow when tapped, about 30 minutes.
-
16
Lift bread from pan and transfer to a rack to cool slightly.
-
17
Cut into roughly 3-inch squares before serving.
-
18
*Available at specialty foods shops and Kalustyan's (800-352-3451).
