Wash the lemons hot and grate them dry. Finely grate the zest of 1 lemon, halve the lemon and squeeze the juice. Cut the remaining lemon into slices and put aside. Peel garlic cloves and chop finely.
Whip 150 g butter with lemon juice, lemon zest and garlic. Season with salt and pepper.
Wash the rosemary, shake dry and pluck roughly. Wash the garlic bulb and cut in half crosswise. Wash the chicken and pat dry, cut open lengthwise on the back side, fold open and press flat.
Spread the chicken on both sides with the seasoning butter. Line a baking tray (approx. 42 x 32 cm) with rosemary and lemon slices, spread the chicken out, with the outside facing upwards, and place it on top.
Add the garlic halves. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 45 minutes.
In the meantime, clean and wash the beans and cut them lengthwise into medium-sized lozenges. Peel and halve shallots and cut into slices. Blanch the beans in boiling salted water for about 4 minutes, pour into a sieve and drain.
Heat 2 tablespoons of butter in a pan and sauté shallots in it, add beans, toss briefly and heat, season with salt and pepper. Take the chicken out of the oven and arrange it, add the beans.