Step 1
Place a rack in middle of oven; preheat to 350°. Season 2 lb. skin-on, bone-in chicken thighs (about 4 medium) on both sides with kosher salt and freshly ground pepper. Pour 3 Tbsp. extra-virgin olive oil into a cold large stainless-steel skillet and swirl to coat bottom of pan. Arrange chicken, skin side down, in pan and place over medium-high heat. Cook undisturbed, rotating pan around on burner often to promote even browning, until skin is browned and chicken releases easily from pan, 7–10 minutes. Transfer to a rimmed baking sheet or large plate and arrange skin side up.
Step 2
Combine 1 large onion, finely chopped, 2 celery stalks, finely chopped, and 2 Tbsp. unsalted butter in same pan and cook over medium-high heat, stirring often, until onion is softened and just starting to turn golden, 8–12 minutes. Add one 6-oz. box instant stuffing mix, ½ cup unsweetened dried cranberries, and 1¼ cups water, then finely grate in zest from 1 lemon and set lemon aside. Mix until stuffing is hydrated. Remove pan from heat and push stuffing to sides to create wells for chicken to rest in. Nestle thighs, skin side up, into stuffing. Transfer pan to oven and bake until chicken is cooked through and top of stuffing is golden brown and crisp, 45–55 minutes.
Step 3
Top chicken and stuffing with more dried cranberries and reserved celery leaves. Cut reserved lemon into wedges and serve alongside for squeezing over.
