Pour the mozzarella into a sieve, drain. Then squeeze between two layers of kitchen paper. Grate cheese. Clean and wash spring onions and cut into fine rings.
Cut bread diagonally (at a distance of approx. 3.5 cm) deep into the bread. Leave the lower part to stand for approx. 2.5 cm. Break open carefully so that the bread does not fall apart. Spread the cut surfaces thinly with 150 g butter. Spread mozzarella, cheese, ham and half of the spring onions evenly into the cuts.
Sprinkle the remaining spring onions (up to 1 tablespoon for garnishing) and the remaining butter in flakes on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 25 minutes. Remove from the oven and serve sprinkled with remaining spring onions.