How to Make It
Combine mustard, preserves, oil and lemon juice in a small bowl. Whisk together well.
Spread 1 side of 4 bread slices with mustard mixture. Top each with a cheese slice. Top each cheese slice with an equal portion of apple slices, another cheese slice and remaining piece of bread.
Melt 1 Tbsp. butter in a large skillet over medium heat. Working with 2 at a time, arrange sandwiches in skillet. Lay a piece of foil on top of sandwiches, then place another heavy skillet (or a pan weighted with cans) on top to press them. Cook until cheese begins to melt and sandwiches are toasted, 2 to 3 minutes per side. Check often during cooking to avoid burning. Wipe out skillet and repeat with remaining butter and sandwiches. Cut each sandwich in half and serve warm.