Preparation

• Heat a 10-inch ovenproof anodized aluminum or nonstick skillet over medium heat. Add the sausage and cook, breaking it up with a wooden spoon, until it’s browned. Add enough olive oil to the fat in the pan to total 2 Tbs., and add the mushrooms and onions. Cook, stirring frequently, until the onions are tender and the mushrooms are browned. Let the mixture cool slightly (it can be warm when added to the eggs, but not piping hot).

  Heat the oven to 350°F. In a bowl, whisk the eggs with the whole milk, flour (don’t worry if the flour forms small lumps), salt, and several grinds of pepper.

  Combine the sausage, mushrooms, onions, Pecorino-Romano, and marjoram with the egg mixture, folding them in gently. Wipe out the skillet and heat 2 Tbs. olive oil over medium heat. When the oil is hot, add the egg mixture, spreading everything evenly. Reduce the heat to low, cover, and cook until the eggs are set about 1 inch in from the sides of the pan, 8 to 12 minutes.

  Uncover the pan and transfer the frittata to the oven. Bake until the top is puffed and completely set, 15 to 25 minutes more.Remove the pan from the oven and run a rubber spatula around the sides of the pan to loosen the frittata. Slip it out of the pan and onto a cutting board. Let the frittata cool for at least 10 minutes before cutting. Serve warm or at room temperature.