Makes 42 squares
2 cups all-purpose flour
2 teaspoons baking powder
¾ teaspoon salt
¾ cup whole milk
¼ cup olive oil
2 Tablespoons (1/4 stick) unsalted butter, melted
2 Tablespoons (1/4 stick) unsalted butter
2 Tablespoons olive oil
3 large onions, thinly sliced (about 2 pounds)
1 Tablespoon finely chopped rosemary
1 teaspoon sugar
½ teaspoon salt
1 ½ cups crumbled blue cheese
FOR THE CRUST
Preheat the oven to 425 degrees.
Mix the flour, baking powder, and salt in a medium bowl to blend. Make a well in the center of the dry ingredients. Whisk the milk, olive oil, and melted butter in a large liquid measuring cup to blend. Slowly pour the milk mixture in the well in dry ingredients, stirring until just blended and smooth. Roll out dough on a lightly floured surface to a 10 x 13-inch rectangle. Transfer the dough to a rimmed baking sheet. Re-form the dough into 10 x 13 –inch rectangle (dough will shrink when moved). Pierce the dough all over with a fork. Let the dough rest while preparing the topping.
Melt butter with oil in a large skillet over high heat. Add the onions. Cook until the onions are soft and beginning to brown, stirring frequently, about 10 minutes. Add rosemary, sugar, and salt. Season onions to taste, with pepper. Reduce heat to medium. Continue to cook until the onions are soft and dark brown, stirring frequently – about 20 minutes; cool.
Spread the onion mixture evenly over the dough. Sprinkle with cheese. Bake until crust is golden brown and cheese is bubbling, about 20 minutes. Let cool and cut into squares.