Hard-Boiled Egg Sandwich

Name: Hard-Boiled Egg Sandwich
Yield: Makes 1
Ingredients: Unsalted butter; 2 slices white bread, toasted, or 1/2 small soft baguette, split horizontally; 2 hard-boiled eggs, peeled and sliced crosswise; Coarse salt and freshly ground pepper; 1 or 2 sprigs watercress