01 - Place chicken thighs in the bottom of the slow cooker in a single, even layer.
02 - In a medium bowl, whisk together the basil pesto, ranch seasoning mix, chicken broth, heavy cream, and grated Parmesan cheese until completely smooth and well combined.
03 - Pour the prepared sauce mixture evenly over the chicken thighs, ensuring all pieces are coated.
04 - Cover and cook on LOW setting for 4 to 6 hours, or until chicken reaches an internal temperature of 165°F and is tender throughout.
05 - Transfer chicken to a serving platter and spoon remaining sauce over the top. Garnish with chopped fresh basil and additional grated Parmesan if desired.