Spread butter evenly on one side of each slice of bread.
Flip the bread over. Spread mustard on the unbuttered side of one slice.
Layer the ingredients on the mustard-coated slice: Swiss cheese, ham, roasted pork, pickles, and the remaining Swiss cheese slice. Top with the second slice of bread, butter-side up.
Heat a heavy skillet, griddle, or panini press over medium heat. If using a skillet, add a small amount of oil or extra butter for better sizzle.
Place the sandwich on the hot surface. If using a skillet, place a heavy weight (like another pan or foil-wrapped bricks) on top of the sandwich to press it.
Cook for 3 to 4 minutes per side until the bread is deeply golden brown and crisp, and the cheese is fully melted. Listen for the sizzle as the butter cooks.
Remove from heat, slice in half diagonally, and serve immediately.
Notes
Use a mixture of butter and a neutral oil for the highest heat and best crisping action.
Pressing the sandwich is key to achieving the authentic texture and melting the cheese evenly.
If you do not have slow-roasted pork, use high-quality deli ham and turkey, though pork is traditional.