Place half of the Canadian bacon in a greased 3-qt. or 13×9-in. baking dish; top with English muffins and remaining bacon. In a large bowl, whisk eggs, milk and onion powder; pour over top. Refrigerate, covered, overnight.
Preheat oven to 375°. Remove casserole from refrigerator while oven heats. Sprinkle top with paprika. Bake, covered, 35 minutes. Uncover; bake 10-15 minutes longer or until a knife inserted near the center comes out clean.
In top of a double boiler or a metal bowl over simmering water, whisk egg yolks, cream, lemon juice and mustard until blended; cook until mixture is just thick enough to coat a metal spoon and temperature reaches 160°, whisking constantly. Reduce heat to very low. Very slowly drizzle in warm melted butter, whisking constantly. Serve immediately with casserole.Yield: 12 servings (1-2/3 cups sauce)