Heat skillet over medium-low heat.
Spread half of the Unsalted Butter (2 tablespoon) on one side of each slice of Sourdough Bread (2 slice). Spread Whole Grain Mustard (1/2 tablespoon) on the side of bread that is facing up.
Place one slice of bread in heated skillet, buttered side down.
Layer half of the sliced Gouda (2 ounce) on top, followed by half of the Apple (1/2) and all of the Deli Turkey (3 slice). Then layer the remaining apple and cheese on top of the sliced turkey.
Spread the remaining Whole Grain Mustard (1/2 tablespoon) on the other unbuttered slice of bread. Place bread onto the sandwich, butter side facing up.
Cook sandwich on medium low heat until bread becomes lightly toasted and golden brown and the cheese begins to melt. About 5 to 8 minutes per side. If the bread begins to brown too fast, reduce temperature.
Once the cheese is melty and the bread is toasted, slice the sandwich in half.