Slice the leek and garlic, then chop the carrot. Peel and cut the celeriac into chunks.
Heat the oil in a large casserole dish. Add the leek, fennel seeds and chicken, then sauté for about 8 minutes.
Meanwhile, set the oven temperature to 170°C.
When the leek is tender and the chicken is lightly browned, add the thyme leaves, carrot and celeriac pieces.
Pour in the chicken stock, then bring to a boil. Cook for about 5 minutes, then add the beans and bring to a boil again.
Cover the dish with a lid, then put it in the oven.
Bake for about 30 minutes, until golden.
Take the dish out of the oven, then add the lemon zest and juice. Reduce the jus over the hob, if necessary.
Serve warm with fresh herbs scattered on top.