Whisk flour into butter melted butter. Preheat oven to 400°F,
Gradually whisk in warm milk, and cook, whisking constantly until thickened.
Whisk in salt, black pepper, 1 cup shredded cheese, and red pepper until smooth. Stir in pasta. Spoon pasta mixture into a lightly greased 2 quart baking dish. Top with remaining cheese. Bake at 400°F for 20 minutes or until golden and bubbly.