Preheat oven to 400°. Let frozen puff pastry sheet stand at room temperature, covered with a cloth towel, 30 minutes or until partially thawed. Unfold pastry sheet on a lightly floured surface. Whisk together egg and milk. Brush pastry sheet with egg mixture, and sprinkle with Parmesan cheese, Cheddar cheese, and chives. Cover pastry with plastic wrap, and gently press cheese and chives into pastry to adhere, using a rolling pin. Remove plastic wrap; sprinkle pastry with salt and paprika. Cut with a 2 1/2-inch round cutter, and place 1 inch apart on a parchment paper-lined baking sheet. Bake at 400° for 10 to 15 minutes or until golden brown. Remove from oven to a wire rack, and cool 5 minutes.