Wash the potatoes and cook them covered with skin for about 20 minutes. Place the ham slices next to each other on a baking tray lined with baking paper. Roast in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for about 10 minutes.
Let it cool down.
Clean the mushrooms and clean them with a brush or kitchen paper, wash briefly if necessary. Depending on the size, leave them whole or halve them. Clean and wash spring onions and cut into fine rings. Quench potatoes cold and let them cool down a little.
Mix vinegar, mustard, honey, salt and pepper. Stir in 4 tablespoons of oil. Peel and slice the potatoes. Mix with spring onions and the vinaigrette.
Heat 2 tablespoons of oil in a frying pan. Fry the mushrooms for about 5 minutes while turning them. Season with salt and pepper. Deglaze with sherry, bring to the boil once. Carefully fold the mushrooms together with the frying stock into the potatoes.
Season to taste with salt and pepper. Break ham slices into large pieces and arrange on the salad.