Step 1: Prepare the Casserole Base

1. Grease a 9×13-inch baking dish with non-stick cooking spray.
2. Spread the cubed and toasted English muffins evenly across the bottom of the dish.
3. Scatter the diced Canadian bacon or ham over the English muffin cubes.

Step 2: Make the Egg Mixture

1. In a large mixing bowl, whisk together the eggs, milk, heavy cream, Dijon mustard, garlic powder, onion powder, salt, and pepper until well combined.
2. Pour the egg mixture evenly over the English muffins and bacon in the baking dish.
3. Press down gently to ensure the bread soaks up the custard.

Step 3: Chill the Casserole

1. Cover the dish with aluminum foil or plastic wrap and refrigerate for at least 4 hours, or overnight for best results.

Step 4: Bake the Casserole

1. Preheat your oven to 375°F (190°C).
2. Remove the casserole from the refrigerator and let it sit at room temperature for 15 minutes.
3. Bake, covered, for 30 minutes. Then, uncover and bake for an additional 10–15 minutes, or until the eggs are set and the top is lightly golden.

Step 5: Prepare the Hollandaise Sauce

1. While the casserole bakes, prepare the hollandaise sauce. In a heatproof bowl, whisk the egg yolks, lemon juice, Dijon mustard, and cayenne pepper (if using) until smooth.
2. Place the bowl over a pot of simmering water, ensuring the bottom of the bowl doesn’t touch the water.
3. Gradually whisk in the melted butter, a little at a time, until the sauce is thick and creamy. Season with salt to taste.

Step 6: Assemble and Serve

1. Drizzle the hollandaise sauce generously over the baked casserole.
2. Garnish with fresh parsley, paprika, or green onions as desired. Serve warm and enjoy!