Crack the eggs into a medium bowl and whisk until the egg whites and yolks are well combined. Season with salt.

Heat an 8-inch nonstick skillet over medium heat. Add a small pat of butter or a drizzle of olive oil to the pan and swirl to coat the bottom. Pour the eggs into the pan and reduce the heat to medium-low. Cook without stirring until the edges just begin to set, about 10 seconds. Working around the edges of the omelette, use a spatula to quickly push the cooked egg toward the center of the pan. Let the uncooked egg run to the outside of the pan, tilting the pan as necessary. Continue until the uncooked egg thickens and fills in the edges of the omelette slowly, then use the spatula to gently smooth the raw egg into an even layer.

Cook without stirring until the omelette is mostly set, then add your desired filling on one side and fold the other side over it. Cook until the eggs are just set. Remove from the heat, season to taste with salt and pepper, and serve.