Wash the potatoes thoroughly and cook for 15-20 minutes. Clean, wash and chop the beans. Steam them covered in little boiling salted water for about 10 minutes. Quench both and drain. Fry bacon until crispy.
Drain on kitchen paper.
For the marinade, lightly caramelise the sugar in the hot bacon fat. Add 150 ml water, vinegar and stock, bring to the boil. Simmer for 3-4 minutes. Season strongly with salt and pepper. Fold in the oil. Cut potatoes in half and mix with the beans into the marinade.
Leave to soak for at least 30 minutes.
Peel and roughly dice the onion. Crumble bacon and feta. Wash basil and pluck off leaves. Mix everything into the potatoes. Leave to stand for about 45 minutes. Flavour again and serve.