Generously season the cubed chicken with salt and pepper.
Place butter in a skillet over medium-high heat, until sizzling. Add seasoned chicken, and brown on both sides, about 5 minutes. (You can also do this right in the crock of many modern slow cookers by using the cooker’s browning function.)
Transfer chicken to a slow cooker and top with potatoes, onion, evaporated milk, chicken base, thyme, poultry seasoning, salt, and pepper. Stir to combine.
Set the cooker to LOW, cover, and let cook 6 hours.
Set cooker to HIGH; whisk cornstarch into 3 tablespoons of water, and stir into the chowder. Add frozen peas and carrots, re-cover, and let cook 1 additional hour.
Meanwhile bake biscuits according to package directions.
Stir Parmesan cheese into the chicken mixture before serving in bowls topped with 2 biscuits each.