01 - Lightly grease a 9x13-inch baking dish using butter or nonstick spray.
02 - Scatter half the English muffin cubes evenly in the prepared dish and top with half the diced Canadian bacon. Repeat layers with the remaining muffins and bacon.
03 - In a large bowl, whisk together eggs, whole milk, heavy cream, Dijon mustard, salt, black pepper, paprika, and melted butter until well combined.
04 - Pour the egg mixture evenly over the layered muffins and bacon, pressing gently to ensure everything is soaked. Cover and refrigerate for at least 2 hours, or overnight for best texture.
05 - Remove the dish from the refrigerator. Preheat oven to 350°F.
06 - Bake uncovered for 40 to 45 minutes, until the top is puffed, golden, and the center is set. Rest 10 minutes before serving.
07 - Combine egg yolks and lemon juice in a heatproof bowl and whisk until pale. Place over a saucepan of simmering (not boiling) water. Whisk constantly while slowly streaming in melted butter. Continue whisking until thickened, then season with cayenne and salt. Remove from heat.
08 - Cut the casserole into portions, plate, and drizzle each serving with warm hollandaise sauce. Serve immediately.