Preheat your crockpot on high and place the trivet in the bottom of the liner.
Remove the chicken from its packaging, rinse it under cold water, and remove any excess fat or skin using kitchen shears or a sharp knife.
Remove giblets from the chicken, rinse again, and pat dry with paper towels.
Rub the BBQ seasoning generously over the chicken, including inside the cavity. Let it rest for 15 minutes.
Quarter the onion and apple. Stuff them into the chicken, placing extra pieces at the bottom of the crockpot.
Tie the rosemary and parsley together with butcher's twine and place inside the chicken.
Place the chicken in the crockpot, add 1 cup of water, and cover with the lid.
Set the crockpot on high and cook for 4 hours. Do not open the lid. The chicken is done when it reaches 165°F in the thickest part.
Optional Thickener: After cooking, separate the chicken broth from excess grease using a fat separator. Let it sit for 5 minutes.
Pour the strained broth into a pan and bring it to a low boil over medium-high heat.
Mix cornstarch with cold broth (or milk) in a jar and shake until dissolved.
Gradually add the cornstarch mixture to the boiling broth, stirring constantly until it thickens.
Continue to stir until the broth reaches a low boil and thickens smoothly.
