In a Dutch oven on the stove top over medium-high heat, heat the olive oil. Add the mushrooms and cook for 3 minutes, until they start to soften. Add the ham and spinach. Cook for another few minutes, until the spinach is wilted.
2 tablespoons extra-virgin olive oil, 8 ounces mushrooms, sliced, 1 cup ham, cooked and diced, 6 ounces baby spinach, chopped
In a large bowl, beat together the eggs and water. Mix in the salt, pepper, and cheese.
8 eggs, 2 tablespoons water, ½ teaspoon salt, ½ teaspoon freshly ground black pepper, 2 cups shredded Swiss cheese
Pour the egg mixture into the pot and cook, scraping the sides with a silicone spatula. When the eggs have started to cook, turn the heat down to low an cook for about 5 minutes, or until the eggs start to set.
Transfer the pot to the oven. Bake for 8 to 10 minutes, uncovered, until the frittata is golden and puffy.
Remove from the oven and let cool for 5 minutes with the lid on, to prevent sticking.
Loosen the edges with a spatula, cut into wedges, and serve.
Don't skip the oil, as your frittata may stick to the bottom of the pot.
Wooden and silicone utensils work best in the Dutch oven. Don't use metal.
Check the frittata periodically as it is baking. Oven temperatures can vary widely, so use the cooking time provided as a guideline, but check to make sure you are not overcooking.
Leftovers can be stored in the refrigerator for a few days and reheated when ready to eat. You can also eat the leftovers chilled or at room temperature.
Don't freeze the leftovers. The freezing and thawing changes the texture and makes the frittata rubbery.