Hot Browns - Appetizer

Ingredients:
1 1/2 tsp finely chopped red onion
1 1/2 Tbs unsalted butter
2 Tbs all-purpose flour
1 1/2 cups milk
a pinch of cayenne
1 Tbs dry Sherry
3/4 cup grated extra-sharp Cheddar
4 slices of homemade-type white bread, toasted lightly
1/2 pound cooked turkey breast, sliced thin
4 thin slices of tomato
8 slices of cooked bacon
1 Tbs freshly grated Parmesan

Directions:
In a small saucepan cook the onion in the butter over moderately low heat, stirring, until it is softened, stir in the flour, and cook the roux, stirring, for 3 minutes. Remove the pan from the heat and add the milk, scalded, in a stream, whisking vigorously until the mixture is thick and smooth. Add the cayenne and salt and pepper to taste and simmer the sauce, stirring occasionally, for 10 to 15 minutes, or until it is thickened to the desired consistency. Strain the sauce through the fine sieve into a bowl and add the Sherry and Cheddar, stirring until the mixture is smooth.
Arrange the toasts in a baking pan and divide the turkey among them.
Top each sandwich with a tomato slice and 2 slices of the bacon and spoon the sauce evenly over the sandwiches. Sprinkle the sandwiches with the Parmesan and broil them under a preheated broiler about 4 inches from the heat for 5 to 7 minutes, or until the tops are brown and bubbly.