Remove the chicken from the refrigerator and let it sit at room temperature for 30 minutes, if possible.

Brush olive oil on the inside of the slow cooker. Place a slow cooker rack (or Instant Pot rack) in the bottom of your slow cooker. Alternatively, you can ball up 3 pieces of aluminum foil and place them on the edges of the slow cooker to create a rack for the chicken to sit on. 

Generously salt and pepper the outside and the inside cavity of your chicken.

Place half of the lemons, garlic, onion and fresh rosemary in the bottom of your slow cooker. And place the remaining aromatics half inside the cavity of the chicken. Tie the chicken legs together with twine.

Rub the softened butter on top of the chicken and (carefully) underneath the skin.

In a bowl, combine paprika, garlic powder, rosemary and onion powder together.

Rub the spices all over the chicken, and place inside of the slow cooker on top of the rack.

Cook on high for 3-4 hours, or low for 6-7 hours until the chicken is fully cooked and tender and has reached a minimum internal temperature of above 165ºF when measured in the thickest part of the thigh. It will likely be much higher.

Preheat broiler to 500ºF.

Carefully transfer the chicken from the slow cooker to a broiler-safe dish. Broil for 4-5 minutes, or until the skin is crispy.

Let rest for 10 minutes before slicing.