Meanwhile, add the prosciutto to a large skillet over medium heat. Cook for about 3 to 5 minutes, stirring occasionally, until crisp around the edges. Transfer the prosciutto to a plate.

Add the butter to the same skillet. Cook over medium heat, swirling or stirring frequently, until the butter foams, turns golden brown, and develops toasted brown flecks, about 4 to 6 minutes.

Add the sage leaves and cook for about 30 to 60 seconds, until fragrant and slightly crisp. Remove a few leaves for garnish if desired.

Reduce the heat to medium-low. Add the garlic and red pepper flakes and cook for about 30 seconds.

Pour in the heavy cream and about 1/4 cup reserved pasta water. Stir and let it gently simmer for 1 to 2 minutes.

Add the drained tortellini and Parmesan. Toss gently until the cheese melts and the tortellini is coated in a glossy sauce. Add more pasta water, a little at a time, until the sauce reaches your desired consistency.

Stir in most of the crispy prosciutto and black pepper. Taste before adding salt since both Parmesan and prosciutto are salty. Finish with the lemon juice, if using. Top with the remaining prosciutto, crispy sage, extra Parmesan, and toasted walnuts or pecans.