01 - Grease a 9x13-inch baking dish thoroughly. Scatter half of the English muffin pieces evenly across the bottom. Distribute half of the Canadian bacon over the muffins. Repeat with remaining muffins and bacon to create even layers.
02 - In a large mixing bowl, whisk together the eggs, whole milk, salt, black pepper, Dijon mustard, and paprika until fully combined and smooth. Pour the egg mixture evenly over the layered muffins and bacon. Gently press down with a spatula to help the bread absorb the liquid.
03 - Cover the baking dish with plastic wrap or foil and refrigerate for at least 1 hour to allow the bread to soak up the custard. For best results and convenient morning preparation, refrigerate overnight.
04 - Preheat your oven to 375°F. Remove the casserole from the refrigerator while the oven heats to take off the chill.
05 - Bake the uncovered casserole for 40 to 45 minutes. The center should be set and firm when gently shaken, and the top should be golden brown. If the top browns too quickly, tent loosely with foil.
06 - While the casserole bakes, create a double boiler by setting a heatproof bowl over a pot of gently simmering water. Whisk together the egg yolks, lemon juice, Dijon mustard, salt, and cayenne pepper in the bowl. Slowly drizzle in the melted butter while whisking constantly until the sauce thickens and becomes smooth. Remove from heat immediately once emulsified.
07 - Let the baked casserole rest for 10 minutes before slicing to allow it to set. Cut into 8 equal portions and serve warm. Drizzle each serving generously with the prepared hollandaise sauce. Garnish with chopped fresh chives or parsley and additional black pepper if desired.