Mastering the French omelette is a rite of passage. It should be pale yellow on the outside (no browning!) and creamy in the center.
- Crack the eggs into a bowl. Season with salt and pepper. Whisk vigorously until the yolks and whites are fully combined and no streaks remain.
- Heat a non-stick skillet over medium-low heat. Add butter and swirl to coat. Do not let the butter brown.
- Pour in the eggs. Use a spatula to constantly stir the eggs while shaking the pan back and forth (like making scrambled eggs) until curds begin to form but the top is still wet.
- Spread the eggs into an even layer. Sprinkle cheese and spinach/mushrooms down the center line.
- Using the spatula, carefully fold one third of the omelette over the filling, then fold the other side over. Tilt the pan to slide the omelette onto a plate, seam side down.