Preheat and position: Preheat oven to 425°F (220°C). Set an oven rack to the center. A hot oven gives the chicken skin a quick blast of heat to render fat and create a golden, crispy skin.

Pat and season chicken: Pat the 600 g chicken thighs very dry with paper towels — removing moisture is critical so the skin crisps rather than steams. Season both sides liberally with 1 1/2 tsp kosher salt and 1 tsp freshly ground black pepper. Tuck 2 smashed garlic cloves and the chopped rosemary (about 2 tsp) under the skin or between the skin and meat where possible so the aromatics sit against the flesh and infuse flavor as the fat renders.

Sear to build color: Heat a large ovenproof skillet (cast-iron works best for even heat) over medium-high heat with 1 tbsp of the olive oil. When shimmering, place the thighs skin-side down and press gently for even contact. Sear without moving for 4–6 minutes until deeply golden and the fat has rendered. Searing develops the Maillard crust — the savory brown layer that gives roast chicken its deep flavor. Transfer the pan off the heat.

Finish roast in oven: Brush the chicken skin lightly with the remaining 1 tbsp olive oil (helpful if the skin looks dry) and roast in the preheated oven for 20–25 minutes (internal temperature should reach 165°F / 74°C at the thickest part). Roasting after searing ensures the inside cooks through gently while the exterior stays crisp.

Prep sweet potatoes while chicken roasts: Peel (if you prefer) and cut the 500 g sweet potatoes into even 1–1.5 inch cubes so they cook evenly. Place in a pot, cover with cold water by 1 inch, add a generous pinch of salt and bring to a simmer. Starting in cold water prevents the outside from overcooking before the center is tender.

Cook sweet potatoes: Simmer the sweet potatoes until fork-tender, about 12–15 minutes. Drain well in a colander and return to the hot pot off the heat for 1 minute to let steam evaporate — this dries the potatoes so the mash will be fluffy, not watery.

Make the mash: Mash the drained sweet potatoes with 2 tbsp (28 g) unsalted butter and 60 ml warm whole milk. Add 2 minced garlic cloves (or 1 clove for a subtler garlic note), and season with 1/2 tsp kosher salt and 1/4 tsp pepper, tasting and adjusting. Mash until smooth but still slightly textured — you want silkiness, not gummy paste. Warm milk and butter incorporate better, keeping the mash hot and glossy.

Blanch the green beans: While the chicken rests, bring a medium pot of salted water to a boil. Add the 300 g trimmed green beans and cook 3–4 minutes until bright green and just tender. Immediately transfer the beans to an ice bath (or run under very cold water) to stop the cooking — this preserves color and crisp-tender texture.

Sauté green beans: In a small skillet over medium heat, melt 1 tsp butter or add a splash of olive oil and warm. Add the blanched beans, 1–2 tsp olive oil (optional), the minced garlic (if you didn't use both in the mash), and sauté 1–2 minutes to warm through and bloom the garlic. Finish with 1/2 tsp lemon zest and 1 tsp lemon juice (optional) and season with salt and pepper. The quick sauté adds a glossy coating and carries the garlicky, bright flavors.

Rest the chicken and finish: Remove the roasted chicken from the oven and transfer to a plate to rest 5 minutes. Resting allows juices to redistribute so the meat stays moist. While resting, spoon a little of the pan juices over the top of each thigh to add flavor and moisture.

Plate and serve: Spoon a generous portion of sweet potato mash onto each plate, place a roasted chicken thigh alongside, and arrange the garlicky green beans. Finish with a small sprinkle of flaky sea salt, extra chopped rosemary if you like, and a grind of black pepper. Serve immediately so the skin stays crisp.