01 - Coat a 9x13-inch baking dish with cooking spray or butter. Distribute half the English muffin pieces evenly across the bottom. Layer half the Canadian bacon on top, then repeat with remaining muffins and bacon to create two complete layers.
02 - Whisk together eggs, milk, heavy cream, Dijon mustard, salt, pepper, and paprika in a large bowl until thoroughly combined and smooth. Pour the mixture evenly over the layered bread and bacon, ensuring all pieces are saturated. Press down gently to help the bread absorb the liquid.
03 - Cover the baking dish tightly with aluminum foil and refrigerate for a minimum of 8 hours or overnight to allow the bread to fully absorb the custard.
04 - Preheat the oven to 375°F. Remove the casserole from the refrigerator and let it stand at room temperature while the oven heats, approximately 20 minutes.
05 - Bake the covered casserole for 30 minutes. Remove the foil and continue baking for an additional 15 minutes until the center is set, the top is golden brown, and the casserole has puffed up.
06 - While the casserole bakes, set a heatproof bowl over simmering water, ensuring the bowl does not touch the water. Whisk egg yolks and lemon juice vigorously until thickened, about 2 minutes. Slowly drizzle in the hot melted butter while whisking continuously until the sauce becomes smooth and creamy. Season with cayenne and salt to taste. Keep warm until serving.
07 - Allow the casserole to rest for 10 minutes before slicing. Serve warm portions drizzled with fresh Hollandaise sauce and garnish with chopped chives and a light sprinkle of paprika if desired.