Cut the celeriac into 3 steaks, each about 2cm thick (keeping any leftover for stocks and soups). Heat the butter and oil in a frying pan and, once foaming, add the celeriac. Cook one side for 5 minutes until really golden. Flip, add the garlic and thyme, and cook the other side until golden, basting with the butter. Pour in the white wine and reduce by half, then pour in the stock. Simmer gently for 15 minutes until very tender and a knife pierces them easily, then remove to a plate. Add the kale and 100ml of water to the pan, and simmer for 5 minutes. Add the beans and heat through.