1. Prepare the Casserole Base

1. Preheat your oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.
2. In a large mixing bowl, whisk together the eggs, milk, Dijon mustard, onion powder, garlic powder, salt, and pepper. Ensure the mixture is smooth and well-combined.
3. Add the cubed English muffins and diced Canadian bacon to the egg mixture. Toss gently to coat all the pieces evenly.

2. Assemble the Casserole

1. Pour the mixture into the prepared baking dish, spreading it out evenly.
2. Cover the dish tightly with aluminum foil and let it rest for at least 15 minutes to allow the bread to soak up the liquid. This step is crucial for achieving a moist, custard-like texture.

3. Bake the Casserole

1. Bake the covered casserole in the preheated oven for 35 minutes.
2. Remove the foil and bake for an additional 15 minutes, or until the top is golden and the casserole is fully set. You can check for doneness by inserting a knife into the center—it should come out clean.

4. Prepare the Hollandaise Sauce

1. While the casserole bakes, make the hollandaise sauce. In a heatproof bowl, whisk the egg yolks and lemon juice until combined.
2. Place the bowl over a pot of simmering water (double-boiler method), ensuring the bottom of the bowl doesn’t touch the water.
3. Slowly drizzle in the hot melted butter while whisking constantly. Continue whisking until the sauce thickens to a creamy consistency.
4. Add Dijon mustard (if using), salt, and pepper. Remove from heat and cover to keep warm.

5. Serve the Casserole

1. Once the casserole is done baking, let it cool for 5 minutes before slicing it into portions.
2. Drizzle the hollandaise sauce generously over each slice. Garnish with fresh parsley and a sprinkle of paprika for added flavor and color.