Pat the chicken dry inside and out with paper towels. A dry surface helps the seasonings stick and the skin crisp up a bit.
In a small bowl, mix paprika, garlic powder, onion powder, thyme, rosemary, salt, and pepper. This will be your dry rub.
Rub the chicken all over with olive oil, then massage the spice blend onto the skin and under the wings for even flavor.
Stuff the cavity with a few lemon slices and, if you like, a couple of garlic cloves for extra aroma.
Place the chicken in the slow cooker breast-side up. Pour in the chicken broth around the sides (not over the skin so you don’t rinse off the rub).
Dot the top with small pieces of butter if using. This helps create a richer finish and can aid in browning a touch.
Cover and cook on low for 6–7 hours, or until the internal temperature reaches 165°F (74°C) in the thickest part of the thigh. If your slow cooker runs hot, start checking at 5.5 hours.
If you’d like crisper skin, you can finish under a preheated broiler for 3–5 minutes, watching closely to prevent burning.
Let the chicken rest for 10 minutes after cooking, then carve and serve with pan juices spooned over the slices.