Preparation Arrange egg bread on work surface. Spread each slice with mustard. Divide Swiss cheese and sliced tomato equally among 3 bread slices; sprinkle with salt and pepper. Form 3 sandwiches by pressing remaining bread slices, mustard side down, atop tomato. Whisk eggs, 2 tablespoons water and sage to blend in medium shallow bowl. Melt butter in heavy large skillet over medium-low heat. Dip both sides of each sandwich into egg mixture and place in skillet. Cook until cheese melts and sandwiches are golden, about 4 minutes per side. Cut sandwiches diagonally in half. Transfer 3 halves to each plate.
Preparation Arrange egg bread on work surface. Spread each slice with mustard. Divide Swiss cheese and sliced tomato equally among 3 bread slices; sprinkle with salt and pepper. Form 3 sandwiches by pressing remaining bread slices, mustard side down, atop tomato. Whisk eggs, 2 tablespoons water and sage to blend in medium shallow bowl. Melt butter in heavy large skillet over medium-low heat. Dip both sides of each sandwich into egg mixture and place in skillet. Cook until cheese melts and sandwiches are golden, about 4 minutes per side. Cut sandwiches diagonally in half. Transfer 3 halves to each plate.