For filling, in a small saucepan, melt the 2 tablespoons butter. Add apple slices and lemon juice. Bring just to boiling; reduce heat. Cover and cook over low heat for 4 to 5 minutes or until apple is almost tender. Stir in brown sugar; add brandy, nutmeg, and cinnamon. Bring to boiling; boil gently, uncovered, for 3 to 4 minutes or until syrup thickens slightly. Keep warm over low heat.
For omelet, in a bowl, beat eggs, water, and salt with a fork until combined, but not frothy.
In an 8- or 10-inch skillet with sloped sides, heat the 1 tablespoon butter until a drop of water sizzles when dropped in the skillet. Lift and tilt the skillet to coat bottom and sides. Add egg mixture to skillet; cook over medium heat. As eggs set, run a spatula around the edge of the skillet, lifting eggs and letting uncooked portion flow underneath. When egg mixture is set, but still shiny, remove from heat.
Spoon some of the filling across center of omelet. Fold sides of omelet over filling. Transfer to a warm plate. Spoon remaining filling on top of omelet. Makes 1 generous serving.