1. Melt the butter in a saucepan and add the milk.
2. Pour the mixture into a bowl and stir in the yeast. Add the rest of the ingredients (reserve a little of the flour). Knead the dough well.
3. Cover the bowl, for example with the lid of a pot and let rise in a warm place for about an hour. Tip the dough out onto a floured surface and knead thoroughly. Add the rest of the flour as needed.
4. Divide the dough into 24 pieces and roll them out into round pizza bases (about 3 inches in diameter). Place the pizza bases on baking sheets lined with parchment.
5. Combine all the ingredients for the tomato sauce.
6. Cut the ham into cubes.
7. Spread tomato sauce on the bases, top with ham and cheese bases and bake in the middle of the oven for approx. 10 min. at 425°F (fan setting).