- 1 tablespoon unsalted butter, plus more for the dish
- 3 hamburger or hot dog buns, split
- 1 tablespoon olive oil
- 1 small yellow onion, thinly sliced
- 3/4 pound sweet Italian sausage, casings removed
- 6 large eggs
- 1 cup milk
- kosher salt and pepper
- 1/4 cup fresh flat-leaf parsley, chopped
- 1 1/2 cups (6 ounces) grated Swiss cheese
- Heat oven to 350° F.
- Butter a 9-by-13-inch baking dish. Tear the buns into large pieces and place in the dish; set aside.
- Heat the oil in a large skillet over medium-high heat. Add the onion and cook for 1 minute. Add the sausage meat to the skillet. Cook, breaking up the sausage with a wooden spoon, until no trace of pink remains, about 10 minutes.
- In a large bowl, whisk together the eggs, milk, ½ teaspoon salt, and ¼ teaspoon pepper. Stir in the cooked sausage and onion along with the parsley and 1 cup of the cheese.
- Pour the mixture over the buns, pressing with a spatula or spoon to submerge them. Sprinkle with the remaining cheese. Bake until the eggs are set, about 35 minutes. Let cool for 5 minutes before serving.