Melt butter in small sauce pan, add flour and stir with a whisk for 60-seconds to form a roux. Slowly add half & half a little at a time whisking constantly. Allow sauce to simmer for a minute while adding cheeses, salt, pepper and hot sauce, reserve.
Building the Croque Monsieur:
Place the bread on a baking sheet and bake in a 400-degree oven for 5 minutes. Flip and bake for an additional two minutes until toasted.
Brush 4 of the toasted bread slices with dijon mustard. Top each with a thick slice of ham and 1/4 cup gruyere cheese. Top each with the second slice of bread. Pour 1/4 cup of mornay sauce over each sandwich. Top with remaining gruyere cheese. Bake in 400-degree oven for 5-minutes. Switch oven heat source from oven to broiler and broil for 2-minutes until cheese turns gorgeously golden brown.
This is a very popular French Classic recipe, think of it as a Grilled Ham & Cheese Sandwich on steroids. Serve with Pomme Frittes.
* you may substitute Swiss cheese for the gruyere
Recipe makes 4 sandwiches.
You may also make these Croque Monsieur smaller and serve them as appetizers.