Heat butter over medium heat in a small saucepan. Add flour and whisk continuously for 2 minutes. Add mustard, Worcestershire sauce, salt, pepper, hot sauce, and beer and continue to whisk until flour mixture is incorporated. Add cream and stir to combine. Add cheese and continue to stir until completely melted. Remove from heat and let cool for 20 minutes to overnight in the refrigerator. When ready to serve, toast bread slices and spread with a heaping 1/3 cup cheese mixture. Broil in the oven or a toaster oven for 2-3 minutes or until bubbly and lightly browned. Serve garnished with sliced scallions.