Peel and wash the potatoes and cook in salted water for about 20 minutes. Mix pesto and crème fraîche. Wash basil, shake dry and remove leaves.
Wash the meat, dab dry and cut each fillet into 8 slices. Cut mozzarella into 12 slices. Place the fillet slices next to each other on the work surface. Season with salt and pepper. Cover half with 1 slice of mozzarella and 2-3 basil leaves.
Place the remaining fillet slices on top as a lid. Carefully wrap 1 slice of ham tightly around each packet.
Heat the oil in a large frying pan. Fry the parcels on each side at medium heat for about 5 minutes.
Drain the potatoes. Add milk and butter. Mash everything finely. Fold the pesto-crème-fraîche into the puree with a fork. Season to taste with salt. Arrange everything.