For the peach sponge cupcake, first wash the peaches, remove the pit and cut the flesh into bite-sized (not too small) pieces.
Sift together the flour and starch. Crumble the sponge cake (in a blitz chopper or in a plastic bag with a pan or meat tenderizer). Grease 4 ovenproof cups. Spread the biscuit crumbs as a base in them.
Beat the sugar, vanilla sugar, eggs and salt over a hot water bath until fluffy. Then continue beating over the cold water bath until the mixture has cooled and has a creamy consistency. Gently fold in flour mixture.
Pour the batter into the prepared cups to a maximum of 3/4 height. Press in one or more pieces of peach, depending on size.
Bake the peach sponge cup cakes at 180 °C in the preheated oven for a few minutes. Serve directly in the cup while still warm.