Mushroom Onion Potato Frittata Bake with Thyme

Steps

1. Preheat the oven to 425°F (220°C) and line a sheet pan with parchment.
2. Toss the potato cubes with half of the olive oil and half of the salt, spread on the sheet pan and roast 20 to 25 minutes, turning once, until golden and tender.
3. While the potatoes roast, heat the remaining half of the olive oil in a large skillet over medium-high heat. Add the mushrooms and cook 6 to 8 minutes until browned and their liquid has cooked off.
4. Add the onion to the mushrooms and cook 5 minutes until soft and lightly golden, then stir in the garlic and thyme for 30 seconds. Remove from the heat.
5. Lower the oven to 375°F (190°C) and grease a 9x13-inch baking dish with a little oil from the skillet or a light film of the pan juices.
6. In a bowl, whisk the eggs, egg whites, milk, black pepper and the remaining half of the salt until smooth.
7. Spread the roasted potatoes in the baking dish, scatter the mushroom-onion mixture over them, then pour the egg mixture evenly on top. Sprinkle with the Parmesan.
8. Bake 25 to 30 minutes until puffed, set in the center and the eggs reach 160°F (71°C).
9. Rest 5 minutes, sprinkle with the parsley, cut into 4 portions and serve.