Bring the chicken to room temperature (20 minutes). Pat the thighs dry with paper towel and season both sides with 1 tsp kosher salt and 1/2 tsp black pepper. Dry skin sears and crisps better; warming the chicken reduces temperature shock in the oven so it cooks evenly.

Preheat the oven to 220°C / 425°F with a rack in the upper-middle position. High initial heat promotes Maillard browning on the skin, producing deep color and savory flavor.

Prepare the potatoes: cut 800 g Yukon Golds into even 2–2.5 cm (¾–1 inch) chunks. Toss in a large bowl with 1 tbsp olive oil, 1 tsp kosher salt, 1/2 tsp black pepper, 1 tbsp chopped rosemary, and 1/2 tsp smoked paprika (if using). Evenly sized pieces cook uniformly; tossing them in oil and salt helps the surfaces dry and crisp in the high heat.

Heat a 12-inch (30 cm) ovenproof skillet over medium-high heat and add 1 tbsp olive oil. When the oil shimmers, add the chicken thighs skin-side down, spacing them so they do not touch. Sear 5–7 minutes without moving them until the skin is deep golden brown. Searing in a hot pan renders fat and creates a crust that protects the meat from drying in the oven.

While the chicken skin browns, toss the potatoes on a rimmed baking sheet in a single layer. After the chicken is well browned on the skin side, flip each thigh and quickly brown the underside for 1–2 minutes—this develops color and flavor on both sides.

Add the potatoes to the same skillet around and between thighs (or arrange them on the baking sheet if your skillet is too crowded). Scatter 4 smashed and sliced garlic cloves, the remaining 1 tbsp rosemary, and the thyme leaves over the potatoes and chicken. Dot the potatoes with 2 tbsp cold butter cut into small pieces—this helps baste the spuds as they roast and adds a glossy, nutty finish.

Transfer the skillet (or baking sheet) to the preheated oven and roast for 30–35 minutes, until an instant-read thermometer inserted into the thickest part of a thigh reads 74°C / 165°F and the potatoes are fork-tender. Roasting at high heat crisps the skin and edges of the potatoes while finishing the interior to tender perfection.

Remove the pan from the oven and transfer the chicken and potatoes to a warm platter, tent loosely with foil to rest for 8 minutes. Resting lets the cooking juices redistribute; cutting immediately will dry the meat.

While the chicken rests, make a quick pan sauce: place the skillet on medium heat (use the stove even if you used a baking sheet—transfer any browned bits to a small saucepan). Add 120 ml chicken stock and the juice and zest of 1 lemon, scraping the pan with a wooden spoon to release browned bits (these are flavor gold). Let it reduce by about half, then swirl in the remaining 1 tbsp olive oil and the pan drippings—if desired, whisk in the small cubes of butter left in the pan bit by bit to finish the sauce and give it sheen. A reduced pan sauce concentrates flavor and ties the dish together.

Taste the sauce and adjust seasoning with a pinch of salt and a grind of pepper. Spoon the sauce over the chicken and potatoes, garnish with a few extra thyme sprigs and a little lemon zest for brightness, and serve immediately. The lemon cuts the richness and lifts the whole plate.