Ingredients

• 2 oz finely grated Parmigiano-Reggiano (1 cup)
• 1/2 cup mayonnaise
• 1 tablespoon minced onion
• 1/8 teaspoon cayenne
• 10 slices firm white sandwich bread
• Special equipment: a 1 3/4-inch round cookie cutter; a small offset spatula

Instructions

1. Put oven rack in upper third of oven and preheat oven to 400°F.
2. Stir together cheese, mayonnaise, onion, and cayenne.
3. Cut out 4 rounds from each bread slice using cutter and arrange on a baking sheet. Bake toasts until tops are crisp and just golden, 3 to 4 minutes. Cool toasts slightly on baking sheet on a rack. (Leave oven on.)
4. Top each toast with a rounded 1/2 teaspoon cheese mixture, spreading to edge with a small offset spatula or knife. Bake toasts until topping is puffed and golden, about 6 minutes.