In a mixing bowl, whisk together the eggs and milk (if using) until well combined. Season with salt and pepper.
2 eggs, 1/4 cup milk, Salt and pepper to taste
Heat olive oil or butter in a non-stick skillet over medium heat.
1 tablespoon olive oil
Add the mushrooms to the skillet and sauté until they are soft and golden brown, about 3-4 minutes. Add the spinach and cook until wilted, about 1-2 minutes.
1/4 cup mushrooms, 1/2 cup spinach
Pour the egg mixture over the vegetables in the skillet. Let it cook undisturbed for a minute or two until the edges start to set.
Gently lift the edges of the omelette with a spatula and tilt the pan to allow uncooked eggs to flow underneath.
When the omelette is almost set, sprinkle cheese on one half (if using), then fold the omelette in half and cook for another minute until the cheese melts.
1/4 cup shredded cheese
Slide the omelette onto a plate and serve hot.
Notes
For a dairy-free version, omit the milk and cheese.
Add your favorite herbs or spices for extra flavor.