11 can (28 ounces) plum tomatoes with puree, or equivalent quantity of marinara sauce
2large yellow onionsthinly sliced (4 to 5 cups)
Freshly ground black pepperto taste
8 to 10ouncesmozzarella, caciocavallo or provolone cheese, or a blendthickly shredded
8 to 10anchovy filletscut in small pieces
Dried oreganoto taste
1/2cupdried breadcrumbsmoistened with olive oil
Lightly coat bottom and sides of a large rimmed baking sheet with olive oil.
Combine yeast and 1 teaspoon sugar with 1 cup warm water in a liquid measuring cup. Let stand for a few minutes, until a beige scum forms on top of the water.
Combine 3 cups flour and 1 teaspoon salt in a large bowl. Combine 1/4 cup olive oil with yeast mixture and add to flour. Using a wooden spoon, gradually mix liquid into flour.
Turn dough onto a granite countertop or other smooth surface; knead, adding up to 1/2 cup more flour if necessary, until dough is glossy and no longer sticky, about 10 minutes; shape into a ball. Clean the bowl and drizzle a little oil into it; turn the dough to coat lightly. Cover and let rise in a warm place for a couple of hours until it more or less doubles in size.
Meanwhile, prepare tomato-onion sauce: Place tomatoes with puree in a blender or food processor. Pulse to a chunky consistency.
Stir onions and 1/4 cup olive oil together in a large skillet. Over medium heat, cook until onions soften, adjusting heat as necessary so they do not brown.
Add pureed tomatoes, 1 teaspoon sugar, 1/2 teaspoon salt and black pepper to taste (omit seasonings if using prepared marinara sauce). Reduce heat and simmer until mixture thickens, 10 to 20 minutes. Remove from heat and cool.
Gently deflate dough with a fist and press it over the bottom and sides of the prepared pan. Spread mozzarella evenly over dough. Dot with anchovy pieces. Cover with tomato-onion sauce, leaving a 1-inch border. Sprinkle with oregano. Sprinkle breadcrumbs moistened olive oil on top. Let rise for 30 minutes to an hour.
Preheat oven to 425°F. Bake sfincione on a rack in lower third of oven until crust edges turn golden brown, 20 to 25 minutes. Let stand for 5 minutes. Cut into squares.