
Preheat oven to 400 degrees F. Lightly oil four 10-ounce ramekins or coat with nonstick spray.
Melt butter in a large skillet over medium heat. Add mushrooms, garlic, thyme and red pepper flakes, if using. Cook, stirring occasionally, until tender, about 3-4 minutes; season with salt and pepper, to taste. Stir in spinach until wilted, about 2 minutes.
Divide mushroom mixture evenly into the ramekins. Top with eggs, heavy cream and Parmesan; season with salt and pepper, to taste.
Place into oven and bake until egg whites are just set, about 10-14 minutes.
Serve immediately.