Peel, wash and dice the potatoes and sweet potatoes separately (approx. 2 cm). Cook the potatoes in a large pot in salted water for about 10 minutes. Add sweet potatoes and continue cooking for about 10 minutes. Drain and let it cool down.
Boil eggs hard, quench, peel and let them cool down. Fry bacon in a pan without fat in portions until crispy. Drain on kitchen paper.
Mix mayonnaise, mustard and vinegar. Season to taste with salt, pepper and a little sugar. Peel and chop the onions. Break the bacon into large pieces. Dice eggs coarsely. Mix whole potatoes, onions, bacon, eggs and dressing in a large bowl. Season to taste with salt and pepper. Leave to stand for about 1 hour.
Wash the basil and cut the leaves finely. Season salad with salt and pepper. Serve with basil.