Preheat the oven to 425°F (220°C). Choose a large sheet pan or a roasting pan so the chicken and potatoes have space to brown.
Pat the chicken dry with paper towels. Dry skin = crisp skin. Set aside.
In a large bowl, combine potatoes, onion, and half the garlic. Add olive oil, lemon zest, half the paprika, thyme, rosemary, half the salt, and pepper.
Toss to coat evenly.
In a small bowl, mix the remaining garlic, paprika, salt, pepper, and melted butter (if using). Rub this mixture all over the chicken pieces. Squeeze in the lemon juice and rub again.
Spread the potatoes and onions on the pan in a single layer.
Nestle the chicken on top, skin-side up. This lets the potatoes soak up the drippings.
Bake for 35–45 minutes, depending on the size of the pieces. The chicken is done when the internal temperature reaches 165°F (74°C), juices run clear, and the skin is golden.
If the potatoes need more browning, remove the chicken to a plate, toss the potatoes, and return the pan to the oven for another 5–10 minutes.
Rest the chicken for 5 minutes.
Garnish with chopped parsley and serve with lemon wedges.