Grease a 9x13-inch baking dish with butter or non-stick spray. Tear the English muffins into bite-sized pieces and layer them evenly across the bottom of the dish.

Chop the smoked ham into small pieces and sprinkle it over the English muffins. Follow with an even layer of shredded cheese.

In a large bowl, whisk together the eggs, half and half, salt, pepper, and mustard powder. Pour this custard evenly over the layers in the baking dish.

Cover the dish tightly and refrigerate for at least 8 hours, or overnight.

Preheat the oven to 350°F (175°C). Remove the cover and bake for 45-55 minutes until golden brown.

Prepare the hollandaise sauce while baking; whisk egg yolks, lemon juice, and melted butter until creamy.

Once baked, let the casserole sit for 5-10 minutes, then drizzle with hollandaise before serving.