Wash duck breasts and pat dry. Fry them vigorously on each side in hot oil. Season with salt and pepper. Fry over medium heat for about 20 minutes. In the meantime, clean and wash the beans.
Cook in boiling salted water for 15-20 minutes. Spread out deep-frozen potato balls on a baking tray. Cook in the preheated oven (electric cooker: 200 °C/ gas: level 3) for 15-20 minutes. After approx. 8 minutes, turn carefully.
For the sauce, wash the orange, peel in fine strips. Peel the orange afterwards, so that the white skin is completely removed. Cut out the fillets between the parting skins. Squeeze juice from the rest of the orange.
Cut the kumquats into slices. Blanch orange peel and kumquats in boiling water for about 2 minutes, drain. Wrap meat in aluminium foil and keep warm. Drain duck fat. Deglaze meat with orange juice and stock.
Add bowl and kumquats, bring to the boil briefly. Stir the starch and a little water until smooth and thicken the sauce. Bring to the boil briefly, heat up the orange filets in it. Season with salt, pepper and liqueur. Cut the duck breast open and serve with some sauce, beans and potato balls.
Serve garnished with lemon slices and lemon balm as desired.