Prepare the pretzels according to package instructions. Stack vertically on a vertical paper towel holder to create a pretzel tower.
Place the cheese, vegetable stock and mustard in a microwave-safe bowl and cover with plastic wrap or a microwave-safe plate. Microwave on medium power until the cheese is melted, 1 to 2 minutes. Whisk until the dip comes together as a smooth sauce.
Serve warm with the pretzel tower, sliced apples, seedless green grapes and extra mustard for dipping.