In a large heavy skillet cook bacon in batches over moderate heat, turning it, until golden brown and crisp
. Transfer bacon, as cooked, to paper towels to drain
Toast bread and if desired, discard crusts and lightly butter toast. Arrange toast on 6 flameproof plates and divide turkey among toasts.
Make sauce: In a 2 to 3-quart heavy saucepan melt
butter over moderately low heat and whisk in flour. Cook roux
, whisking constantly, 3 minutes. Add 2 cups milk in a stream, whisking, and bring sauce to a boil, whisking. Simmer
sauce, whisking occasionally, 5 minutes.
While sauce is simmering, in a bowl, whisk
together the egg yolk and remaining 1/2 cup milk. Whisk about 1 cup sauce into yolk mixture. Remove pan from heat and whisk yolk mixture into sauce with Parmesan
. Cook sauce over moderately low heat, whisking constantly, until a thermometer registers 160 degrees F. Remove pan from heat and season sauce with white pepper
and salt. In a small bowl whisk cream until it just holds stiff peaks and stir into sauce.
Spoon sauce evenly over turkey and sprinkle Parmesan evenly over sauce. Broil
sandwiches in batches about 2 to 3 inches from heat until sauce is lightly browned, about 2 minutes.
Arrange 2 bacon slices in an X on each serving.