01 - Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - Arrange half of the English muffin cubes evenly in the baking dish. Sprinkle with half of the diced Canadian bacon. Repeat layering with remaining muffins and bacon.
03 - In a large mixing bowl, whisk together eggs, whole milk, heavy cream, Dijon mustard, salt, black pepper, paprika, and melted butter until fully combined.
04 - Pour the egg mixture evenly over the muffin and bacon layers, pressing gently to ensure all ingredients are submerged.
05 - Cover the baking dish and refrigerate for at least 2 hours or overnight for optimal absorption.
06 - Preheat the oven to 350°F. Remove casserole from refrigerator while the oven heats. Bake uncovered for 40 to 45 minutes until puffed, golden, and the center is set. Let rest 10 minutes before slicing.
07 - In a heatproof bowl, whisk together egg yolks and lemon juice until slightly thickened. Set the bowl over a saucepan of simmering water, making sure the base does not touch the water. While whisking, gradually stream in warm melted butter. Whisk continuously until the sauce thickens. Season with cayenne and salt. Remove from heat.
08 - Cut the casserole into portions, plate each serving, and spoon hollandaise sauce over the top. Serve immediately.