Preheat oven to 375 degrees F. Brush a large 9x13-inch baking dish with melted butter and set aside.

Working with one croissant at a time, split open with a serrated knife, not cutting all the way through. Spread the inside with mustard, and fill with two half slices of cheese, and two slices of ham. Place the mini sandwich in the prepared baking dish. Repeat with the remaining croissants, filling and lining them up snuggly in the baking dish.

In a very large measuring glass or bowl, whisk together the eggs, whole milk, heavy cream, garlic, onion, paprika, parsley, salt and pepper until evenly combined. Carefully pour into the baking dish, avoiding the tops of the sandwiches directly. Brush the tops of the croissants with the rest of the melted butter and sprinkle with the bagel seasoning.

Cover with plastic wrap and chill for at least 1 hour or overnight. Remove the plastic wrap and bake until golden brown and the eggs have puffed and are no longer runny in the center, about 45 minutes to 1 hour. Remove from the oven and sprinkle with parsley. Cut and serve immediately. Enjoy!