Peel the jacket potatoes and cut into cubes. Cut the bell pepper and shallot into fine cubes, celery and spring onions crosswise into fine slices. Core the peppers and cut them into very fine cubes. Finely chop the garlic cloves.
Mix the potatoes with the vegetables, shallots, peppers, garlic and herbs. Season to taste with salt.
Mix the mayonnaise with the cream, mustard and sugar and pour over the salad ingredients. Then mix everything well and refrigerate for at least 30 minutes.