Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with unsalted butter.

Cut the English muffins into quarters, toss in melted butter, and toast in the oven for 8-10 minutes until golden brown.

Spread half of the toasted muffin pieces in the baking dish, layer with half of the cooked bacon and sprinkle with 1 cup of Gruyere cheese. Repeat layers.

Whisk together eggs, whole milk, heavy cream, Dijon mustard, salt, black pepper, garlic powder, and cayenne pepper in a mixing bowl.

Pour the egg custard evenly over the layers and let sit for 20 minutes at room temperature.

Bake the casserole for 45-55 minutes until golden on top. Let it rest for 10-15 minutes before slicing.

For the hollandaise sauce, melt butter, and let it cool. Blend egg yolks, lemon juice, Dijon mustard, and salt until frothy.

Drizzle warm melted butter into the blender while running at low speed until hollandaise thickens.

Taste and adjust seasoning. If too thick, add hot water to desired consistency.

Serve the casserole with hollandaise drizzled on top, garnished with chives, parsley, and paprika.