Heat half of the oil in a large skillet over medium heat. Add the onion, salt, and cook, stirring, until softened, 4-5 minutes. Add the shredded Brussels sprouts and stock and cook over medium high heat until liquid reduces by half, 4-5 minutes. Add the Brussels sprouts leaves, season with salt and pepper to taste, toss to combine and keep warm. Cook the Tortelloni according to package instructions and drain, reserving ½ cup of the pasta cooking water. Add the Tortelloni to skillet and gently toss; add half of the cheese and remaining oil and gently toss again, adding the reserved pasta cooking water a little at a time to loosen the sauce if needed.
Divide Tortelloni among plates. Garnish with extra cheese shavings if desired and serve.
You can make this recipe also with Cheese Lovers Tortelloni or Prosciutto & Cheese Tortelloni