Even people who don't care for spinach can't pass up these satisfying appetizer squares. They're a hit as a deliciously different vegetable side dish as well. —Patricia Kile, Elizabethtown, Pennsylvania
Brush the bottom and sides of a 13x9-in. baking dish with 1 tablespoon butter; set aside. In a large bowl, combine the flour, baking powder, seasonings, eggs, milk and remaining butter. Stir in the spinach, cheeses and onion. Spread in prepared pan.
Bake, uncovered, at 350° for 30-35 minutes or until a toothpick inserted in the center comes out clean and edges are lightly browned. Cut into squares. Garnish with pimientos if desired.