Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the potatoes and chop into chunks around 1cm across. Toss in a bowl with ½ tbsp oil, some salt and pepper. Spread out on a baking tray and slide into the oven. Roast for 10 mins.
Zest and juice the lemon. Peel and grate or crush 1 garlic clove. Whisk together in a small bowl. Finely chop the rosemary leaves and add those too. Season.
Pop the chicken in a small baking dish. Pour over the lemon, garlic and rosemary marinade. Add 100ml cold water. Cover with foil. Move the potatoes down to the middle shelf of the oven and put the chicken on the top shelf. Bake for 30 mins. The chicken should be white and the juices run clear when pierced with a skewer. The potatoes will be golden and crisp.
Meanwhile, tear the kale leaves from their tough stalks. Peel and grate or crush the remaining garlic clove. Whisk the garlic clove with 1 tsp oil, 1 tsp fennel seeds and some seasoning.
Pop the kale leaves into a bowl and pour over the garlic oil. Massage this into the kale leaves. Spread out on a lined baking tray. Drain and rinse the butter beans.
After the chicken has cooked for 30 mins, remove the foil and tip the beans into the baking dish. The potatoes should be ready by now, so tip them into a serving dish, cover with foil and keep warm in the bottom of the oven.
Cover the chicken dish again and slide back into the oven. Put the kale on the shelf below the chicken. Bake for 5 mins. The kale should just be starting to brown at the edges.
Serve the chicken with the potatoes, crisped kale, butter beans and the lemony garlic juices.