- Grease a 9x13-inch baking dish. Scatter half the English muffin pieces across the bottom. 
- Layer with half the chopped Canadian bacon. Repeat with remaining muffin pieces and bacon. 
- In a bowl, whisk eggs, 2 cups milk, onion powder, salt, and pepper. Pour the mixture evenly over the muffins and bacon. 
- Cover and refrigerate for at least 8 hours or overnight. 
- Preheat the oven to 375°F. Bake uncovered for 40–45 minutes or until the eggs are set. 
- Meanwhile, make the hollandaise sauce: melt butter in a saucepan, whisk in the sauce mix and 1 cup milk, and cook until thickened. 
- Drizzle the warm hollandaise over the baked casserole before serving.