Wash the potatoes, wrap in aluminium foil and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 1 1/2 hours. Wash thyme and parsley and dab dry.
Set aside 4 stems of parsley for garnishing. Pluck the remaining leaves from the stems and chop them. Wash, clean, quarter and seed the tomatoes. Cut the flesh into small cubes. Clean and wash spring onions and cut into fine rings.
Set aside 1 tablespoon each of the diced tomatoes and onion rings for sprinkling. Stir the quark until smooth. Fold in diced tomatoes, spring onion and herbs. Season quark with salt, pepper, a little sugar and lemon juice.
Heat the oil in a small, coated pan. Leave the ham in it until crispy. Remove the potatoes, wrap them in foil and let them cool down a little. Cut the potatoes lengthwise in the middle, press them apart and add the herb curd cheese.
Sprinkle with spring onions, diced tomatoes and ham. Garnish with the remaining parsley.