01 - Lightly grease a 9x13-inch baking dish with unsalted butter or nonstick spray.
02 - Arrange half the cubed English muffins evenly in the dish and sprinkle with half the diced Canadian bacon. Repeat layering with remaining muffins and bacon.
03 - In a large bowl, whisk together the eggs, whole milk, heavy cream, Dijon mustard, salt, black pepper, paprika, and melted butter until well combined. Evenly pour mixture over the layered muffins and bacon, gently pressing down to ensure all pieces are submerged.
04 - Cover the dish with plastic wrap and refrigerate for at least 2 hours or overnight for optimal flavor and texture.
05 - Preheat oven to 350°F. Allow the casserole to sit at room temperature while the oven heats.
06 - Bake uncovered for 40 to 45 minutes until the surface is puffed and golden and the center is set. Let rest for 10 minutes before slicing.
07 - For the hollandaise, whisk egg yolks and lemon juice in a heatproof bowl until light. Set bowl over a saucepan of gently simmering water, ensuring the bottom does not touch the water. Whisk constantly while slowly streaming in the melted warm butter until the sauce thickens. Season with cayenne pepper and salt. Remove from heat.
08 - Slice baked casserole, plate individual portions, and drizzle generously with warm hollandaise. Serve immediately.