Top 3 tortillas equally with pepperoni, tomatoes and cheese. Top with remaining tortillas.
In 12-inch nonstick skillet, melt 1 tablespoon of the butter over medium heat; rotate skillet so butter coats bottom of skillet. Cook 1 quesadilla in butter 6 to 8 minutes, turning once, until lightly browned. Remove from skillet; place on cutting board.
Repeat with remaining butter and quesadillas. Cut each quesadilla into 16 square pieces. Serve with warmed pizza sauce.