Mushroom Onion Potato Gratin Egg Bake

Steps

1. Preheat the oven to 375°F (190°C) and brush an 8x8-inch baking dish with a little of the olive oil, taking it from the half you'll use in the skillet.
2. Heat half of the olive oil in a large skillet over medium-high heat. Add the mushrooms and cook 6 minutes until browned, then add the onion and cook 6 minutes more until soft and golden.
3. Stir the garlic and the thyme into the skillet for 1 minute, then add the spinach and stir until just wilted. Take the skillet off the heat.
4. In a large bowl, toss the potato slices with the remaining half of the olive oil and half of the salt.
5. In a second bowl, whisk the eggs, ricotta, milk, half of the parmesan, the remaining half of the salt and the black pepper into a smooth custard.
6. Layer half of the potato slices in the dish, spread all of the mushroom-onion mixture over them, then top with the remaining half of the potato slices.
7. Pour the custard evenly over the layers, pressing the potatoes down so they are mostly covered. Sprinkle the remaining half of the parmesan over the top.
8. Cover with foil and bake 30 minutes, then uncover and bake 20 to 25 minutes more, until the potatoes are tender when pierced, the top is golden and the center reaches 160°F (71°C).
9. Rest the bake 10 minutes so it sets, then sprinkle with the parsley, cut into 4 pieces and serve.