01 - Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
02 - Evenly layer half of the English muffin pieces in the prepared dish. Top with 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 melted butter until well combined.
04 - Pour the egg mixture evenly over the muffin and bacon layers. Gently press down to ensure the bread soaks up the liquid.
05 - Cover with foil and refrigerate for at least 1 hour, or overnight for best texture.
06 - Remove from refrigerator and let sit at room temperature while oven preheats. Bake covered for 30 minutes.
07 - Remove foil and bake an additional 15 minutes, until set and slightly golden.
08 - Meanwhile, make the hollandaise: In a heatproof bowl, whisk yolks and lemon juice until combined. Place over a saucepan of barely simmering water (double boiler), whisking constantly.
09 - Slowly drizzle in melted butter, whisking until the sauce thickens, about 5 minutes. Stir in Dijon, season with salt and pepper, and remove from heat.
10 - When casserole is done, let it rest 10 minutes. Slice and serve warm, drizzled generously with hollandaise sauce.