Layer the base: Add chicken breasts to the bottom of the crockpot.
Sprinkle with salt, pepper, Italian seasoning, onion powder, and garlic.
Pour the sauce: Stir together Alfredo sauce, heavy cream, and chicken broth in a bowl. Pour over the chicken. Add butter if using.
Cook the chicken: Cover and cook on Low for 3.5–4.5 hours or High for 2–3 hours, until the chicken is tender and easily shreds.
Shred and enrich: Remove chicken to a plate and shred with two forks.
Stir grated Parmesan into the sauce, then return the chicken to the crockpot.
Add tortellini: Stir in the refrigerated tortellini, making sure it’s submerged in sauce. Cook on High for 20–30 minutes, just until tortellini is tender.
Taste and finish: Adjust salt and pepper. The sauce will thicken as it stands.
Garnish with parsley and extra Parmesan. Serve hot.