Season chicken pieces generously with salt and black pepper. Heat a 5-6 quart pot over medium-high heat and melt 4 tablespoons butter until it starts to foam. Add the chicken in a single layer and cook for 6-8 minutes, stirring occasionally, until browned on all sides and the internal temperature reaches 165°F with no pink remaining. Remove the chicken to a plate and set aside.

In the same pot, add the remaining 1 tablespoon butter if the pot looks dry. Toss in the minced garlic and sauté for just 30 seconds until fragrant but not browned. Add the red pepper flakes and stir to release their flavor.

Pour in the chicken broth, scraping up any browned bits stuck to the bottom of the pot with a wooden spoon. Stir in the heavy cream and bring the mixture to a gentle simmer. Keep the heat at medium to prevent the cream from curdling.

Add the fresh tortellini to the simmering sauce and cook for 4-6 minutes, stirring frequently to prevent sticking. The tortellini should become tender when tested with a fork. If using frozen tortellini, add an extra 1-2 minutes of cooking time.

Return the cooked chicken to the pot along with any accumulated juices. Stir in the grated Parmesan cheese until completely melted and the sauce becomes silky and glossy. Let everything simmer together for 2-3 minutes so the chicken warms through and absorbs the sauce flavors.

Turn off the heat and toss in the fresh chopped herbs. Give everything a final gentle stir to distribute the herbs throughout. Taste and adjust seasoning with additional salt, pepper, or red pepper flakes as needed. Serve immediately while hot, with extra Parmesan on the side.