01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Layer half of the English muffin pieces in the dish, followed by half the Canadian bacon. Repeat with remaining muffins and bacon.
03 - In a large bowl, whisk together eggs, milk, Dijon mustard, salt, pepper, paprika, and 2 tablespoons melted butter until fully blended.
04 - Pour the egg mixture evenly over the casserole. Gently press down on the bread to ensure it absorbs the liquid.
05 - Cover with aluminum foil and refrigerate for at least 1 hour, or overnight, to allow the flavors to meld.
06 - Bake covered for 30 minutes. Remove the foil and continue baking for an additional 15 minutes until the center is set and the top is golden.
07 - Whisk egg yolks and lemon juice in a heatproof bowl over a saucepan of simmering water. Slowly drizzle in ½ cup melted butter while whisking constantly until thickened, about 5 minutes.
08 - Stir in the Dijon mustard and season with salt and pepper to taste. Remove from heat.
09 - Allow the casserole to rest for 10 minutes before slicing. Serve warm, drizzled generously with the hollandaise sauce.