Cheesy Spinach Dip Pasta Bake

Place oven rack in middle of oven; heat oven to 425 °F. Cook 1 box (12 oz) penne pasta in boiling salted water as directed on box until al dente. Drain; transfer pasta to large bowl. Add 2 boxes (10 oz each) frozen chopped spinach, thawed and squeezed to drain well, 2 jars (15 oz each) Alfredo sauce, 1 teaspoon crushed red pepper flakes and 2 cups of the shredded mozzarella cheese to pasta; stir to combine. Season with salt and pepper to taste. Pour pasta mixture into ungreased 13x9-inch (3-quart) glass or ceramic baking dish. Sprinkle remaining 1 cup shredded mozzarella cheese evenly over top. Bake on middle oven rack about 20 minutes or until bubbly. Turn oven control to broil. Leaving baking dish on middle oven rack, broil pasta bake until lightly browned on top. Cool slightly before serving.