Heat a cast-iron skillet over medium heat and cook bacon until crisp, about 4 minutes on each side. Remove bacon from skillet and place on a lined paper towel.
Butter one side of each slice of bread. Spread the Nutella evenly on the opposite side of two buttered bread slices. Spread the mascarpone cheese on the opposite sides of the remaining two slices of buttered bread. Assemble each sandwich with 4 pieces of bacon and banana slices. Top with bread, buttered-sides facing out.
Return your cast-iron skillet to medium heat and cook your sandwich on each side until golden brown, about 3 minutes per side. Remove the grilled cheese from your skillet, slice in half, and serve. Cook with soul. Eat with pleasure.