Beat the eggs with the milk and a pinch of kosher salt until the eggs are quite loose and uniform in colour. Return the pan to the burner, this time dropping the heat to low. Let 1 tablespoon of the butter melt in the pan. Pour the beaten eggs into the pan, gently stirring and lifting the cooking egg with a silicone spatula/scraper and tilting the pan to allow the uncooked liquid egg to flow under that which has already cooked. Do this until the egg is mostly scrambled with a touch of liquid egg still remaining on top. Add the spinach to the center third of the omelet, sprinkle the chopped ham on top, and lay one slice of the LAND O LAKES® Deli American Cheese over it. Fold the empty top and bottom 1/3 of the omelet over the filling and slide the omelet out onto the cheese covered piece of bread. Top with the remaining two slices of deli American cheese. Lay the remaining slice of sandwich bread on top. While 1/2 tablespoon of the remaining butter melts in the pan over medium low heat, spread the final 1/2 tablespoon of butter over the top slice of sandwich bread. Carefully transfer the sandwich to the hot pan. Cook until the bottom slice of bread is golden brown. Using your hand to hold the sandwich together, ease a spatula under the sandwich and flip it over gently, continuing to cook until the bottom slice of bread is also lightly golden brown. Add a 1/2 teaspoon of water to the pan, put a tight fitting lid on, and raise the heat to high. This will help melt the cheese. Remove the lid and let the steam escape, cooking 1 more minute to recrisp the bottom slice of bread. Transfer to a cutting board and cut in half before serving piping hot.