Step 1

Preheat a panini press or a large cast iron skillet or griddle over medium heat. Lay bread, open side up, on a work surface and spread the bottom and top halves with mustard. Layer bottom and top halves with Swiss cheese. Working only on bottom halves, layer on all of the pickles, ham, roast pork, and salami (if using). Close sandwiches, pressing gently.

Step 2

Butter top and bottom of panini press and press sandwiches with moderate pressure until crisp on both sides, about 8 minutes. If using a cast iron skillet or griddle, melt half of butter in pan and add sandwiches. Use a second pan to press on them as the first side crisps. When crisp, flip sandwiches, add remaining butter, swirl to coat, and continue cooking while pressing until crisp on both sides, about 10 minutes total. Slice sandwiches in half diagonally and serve immediately.