Place two pieces of bread onto a plate or other flat surface.
Spread raspberry jam on one slice of bread, followed by brie and prosciutto. Sprinkle mozzarella cheese on top of prosciutto.
Place second slice of bread on top of mozzarella layer. Spread 1 tablespoon of softened butter evenly over the top of bread, coating to the edges.
Place the sandwich, buttered side down, on a medium griddle pan or skillet. Butter the slice of bread that is facing up.
Cook sandwich over medium heat, 3-4 minutes per side, or until crust is golden and cheese starts to melt.