Preheat the oven to 350°F, 177°C, or gas mark 4.

In a large mixing bowl, whisk together the eggs, heavy cream, salt, and pepper, then add the shredded gouda, stir and set aside.

On medium high heat on the stove heat the oil in the cast iron skillet. Add the mushrooms and cook for 2-4 minutes without moving to allow for a nice crust. Stir to flip over and allow to cook on the other side for as long. Once the mushrooms are cooked add the tomatoes and cook until soft, about 2 minutes stirring. Add the garlic and spinach. Cook until the spinach has wilted and released it's water.

Remove from the heat and pour in the egg mixture. Bake for 10 - 15 minutes or until the top starts to brown and the middle is set and does not wobble.