Prosciutto, Brie and Apple Panini with Scallion Butter

plus 2 teaspoons unsalted butter, softened

scallion, finely chopped

fresh lemon juice

Dijon mustard

soft hero or ciabatta rolls, or 1 long baguette, halved lengthwise

thinly sliced prosciutto

Brie, rind removed, cheese cut into 4 pieces

large Granny Smith apple—peeled, cored and thinly sliced