01 - Grease a 9x13-inch baking dish. Scatter half of the English muffin pieces evenly in the dish. Top with half of the Canadian bacon. Repeat with remaining muffins and bacon to create two complete layers.
02 - In a large bowl, whisk together the eggs, milk, salt, black pepper, Dijon mustard, and paprika until thoroughly combined. Pour the mixture evenly over the muffin and bacon layers. Press gently with a spatula to ensure the bread absorbs the egg mixture.
03 - Cover the dish with plastic wrap or aluminum foil. Refrigerate for at least 1 hour, or overnight for best results. This allows the bread to fully absorb the custard and ensures a uniform texture.
04 - Preheat oven to 375°F. Remove the casserole from the refrigerator while the oven heats to allow it to come closer to room temperature for even baking.
05 - Bake the uncovered casserole for 40–45 minutes, until the center is completely set and no longer jiggles, and the top is golden brown. A knife inserted in the center should come out clean.
06 - While the casserole bakes, melt the butter in a small saucepan. In a heatproof bowl over a pot of gently simmering water, whisk together egg yolks, lemon juice, Dijon mustard, salt, and cayenne. Slowly drizzle in the melted butter, whisking constantly until thickened and smooth. Remove from heat immediately.
07 - Let the baked casserole rest for 10 minutes before slicing to allow the layers to set. Slice into 8 portions and serve warm, drizzled generously with hollandaise sauce. Garnish with fresh chives or parsley if desired.