Gather all ingredients on your countertop.

Spread unsalted butter generously on one side of each slice of sourdough bread.

On the unbuttered side of two slices, layer turkey evenly, spread Dijon mustard, and top with Swiss cheese.

Assemble sandwiches with the remaining slices (buttered side out) and press down gently.

Heat a skillet over medium heat and grill sandwiches for 3-4 minutes per side until golden brown and the cheese has melted.

Cut sandwiches in half or quarters and serve hot.