Preheat the oven to 375 degrees F, and line a sheet pan with parchment paper
Prepare the herb butter by combining all the ingredients together in a small bowl.. (Herb butter will keep well, wrapped tightly, in the refrigerator for a week or in the freezer for up to a month.)
Slice the baguette on the bias about 1/2-inch thick. Spread the herb butter on both sides of the baguette slices and arrange in 1 layer on the prepared sheet pan. Toast in the oven until golden brown and crisp on both sides, flipping halfway through, about 15 minutes.
Cover each crostini with 1 tablespoon pasta sauce. Top each with a slice of mozzarella and a meatball. Finish with another tablespoon of pasta sauce. Bake in the oven until the meatballs are warmed through and the cheese has melted, about 15 minutes. Top with a sprinkle of Parmesan and serve hot.