Butter each slice of bread on one side, all the way to the edges then set aside.
2 slices bread, 1 tablespoon salted butter
Place one slice of prosciutto onto your work surface, then place one slice of buttered bread on top - butter-side down.
2 slices prosciutto
Top the bread with sliced mozzarella, then spread the basil pesto (2 tsp) roughly over the cheese.
4-8 slices fresh mozzarella, 2 teaspoon basil pesto
Top with sliced tomato and season with salt and pepper, then top with an additional layer of sliced mozzarella if using.
4-6 slices tomato, salt and pepper
Place second slice of buttered bread on top, butter-side up.
Place the second slice of prosciutto over the top of the sandwich, then fold the ends of prosciutto over each other to enclose.
Heat a panini press, then grill sandwich until cheese has melted and the prosciutto is crisp.