Preparation Preheat broiler. Wrap ham tightly in foil and put on rack of oven farthest from broiler to heat through, about 15 minutes. Meanwhile, melt butter in a heavy medium saucepan over medium-low heat until foam subsides, then whisk in flour and cook, whisking, 1 minute. Whisk in milk, mustard, and 1/4 teaspoon pepper and bring to a boil over medium heat, whisking. Simmer, whisking, 2 minutes, then add beer and simmer, whisking, 1 minute. Remove from heat and whisk in cheese until melted. Arrange bread in 1 layer on a baking sheet and broil 4 to 5 inches from heat, turning once, until lightly toasted, about 5 minutes total. Transfer bread to plates and spoon some of sauce over it, then top with ham and remaining sauce.
Preparation Preheat broiler. Wrap ham tightly in foil and put on rack of oven farthest from broiler to heat through, about 15 minutes. Meanwhile, melt butter in a heavy medium saucepan over medium-low heat until foam subsides, then whisk in flour and cook, whisking, 1 minute. Whisk in milk, mustard, and 1/4 teaspoon pepper and bring to a boil over medium heat, whisking. Simmer, whisking, 2 minutes, then add beer and simmer, whisking, 1 minute. Remove from heat and whisk in cheese until melted. Arrange bread in 1 layer on a baking sheet and broil 4 to 5 inches from heat, turning once, until lightly toasted, about 5 minutes total. Transfer bread to plates and spoon some of sauce over it, then top with ham and remaining sauce.