Cook the Tortelloni according to package directions until al dente; drain.
Heat the butter and sage in a large skillet over medium heat until the butter is just melted.
Add the Tortelloni 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 Tortelloni among bowls and serve with the crostini on the side.