Place 1 cup (250 mL) of the ham on the bottom of a greased 8 inch square (2 L) baking dish. Top with English muffin and scatter remaining ham overtop.
In a bowl, whisk eggs, milk, dry mustard, paprika and pepper. Pour overtop of English muffins and ham. Cover and refrigerate overnight.
Preheat oven to 350°F (180°C). Bake until tester comes out clean, 60 to 70 minutes.
Meanwhile, in blender combine egg yolks, dry mustard, hot sauce and lemon juice. With blender running, slowly pour in the butter in a steady stream. Blend until thickened, 5 to 10 seconds. If sauce is too thick, add 1 to 2 tbsp hot water.
Serve over casserole. Sprinkle with paprika, if desired.