Cook the Tortellini according to package directions until al dente; drain. Heat the butter and sage in a large skillet over medium heat until the butter has melted.
Add the Tortellini to the skillet, add the Parmigiano Reggiano cheese, toss and season with salt and pepper to taste.
Top the crostini with the prosciutto. Divide the Tortellini among bowls and serve with the crostini on the side.