Crack the eggs into a glass mixing bowl and beat them until they turn a pale yellow color.
Heat a heavy-bottomed nonstick sauté pan over medium-low heat. Add the butter and let it melt.
Add the milk to the eggs and season to taste with salt and white pepper. Whisk. When the butter in the pan is hot enough to make a drop of water hiss, pour in the eggs. Let the eggs cook for up to a minute or until the bottom starts to set.
With a heat-resistant rubber spatula, gently push one edge of the egg into the center of the pan, while tilting the pan to allow the still liquid egg to flow in underneath. Repeat with the other edges, until there's no liquid left.
Your eggs should now resemble a bright yellow pancake, which should easily slide around on the nonstick surface. If it sticks at all, loosen it with your spatula.
Now gently flip the egg pancake over, using your spatula to ease it over if necessary. Cook for another few seconds, or until there is no uncooked egg left. Layer cheese, tomatoes, and prosciutto slices on one half of the “egg pancake.” With your spatula, lift one edge of the egg and fold it across and over, so that the edges line up. Cook for another minute or so, but don't overcook or allow the egg to turn brown. If necessary, you can flip the entire omelet over to cook the top for 30 seconds or so. Just don't let it get brown.
Gently transfer the finished omelet to a plate. Garnish with chopped fresh herbs if desired.