- 8 slices of seeded Jewish rye bread
- Unsalted butter, softened, for brushing
- 1/2 cup homemade mustard
- 1 pound thinly sliced mortadella
- 1/2 pound Robiola Bosina cheese, cut into 12 equal slices with the rind
- 1 cup lightly packed baby arugula
- 1/4 cup pickled red onion slices or 12 pickled cocktail onions, thinly sliced
Preheat a panini press or a griddle. Brush one side of each bread slice with butter and arrange buttered side down on a work surface. Spread each bread slice with 1 tablespoon of the mustard. Layer the mortadella, Robiola, arugula and pickled onions on 4 of the bread slices and close the sandwiches.
Grill the panini over moderate heat until browned and crisp outside, about 3 minutes in a press or 3 minutes per side on a griddle. Cut the panini in half and serve.