Cream the butter, icing sugar and salted egg yolk or powder until light and fluffy. Sift in all the flours (milk powder, potato starch and plain flour). Fold until it forms a pliable dough. Transfer to a lightly floured surface. Roll to about 1 cm thickness.
Use your preferred mould to mould the dough. Transfer to the baking tray. Egg wash and sprinkle with some sesame seeds. Bake in the pre-heated oven for 12-15 minutes at 165°C.