Prepare the sponge cake and allow it to cool completely. Slice into 4 even layers using a serrated knife.
In a large bowl, whip the cream, sugar, vanilla, and optional milk powder until medium peaks form.
Gently fold in the Greek yogurt until just combined.
Toss diced peaches with sugar in a small bowl.
Assemble the Peaches and Cream Cake:
Place one cake layer on a serving plate and spread a quarter of the cream.
Add the second layer and spread one-third of the remaining cream.
Add diced peaches evenly.
Place the third layer and spread half of the remaining cream.
Add the final layer and spread the rest of the cream on top.
Decorate with sliced peaches.
Refrigerate until ready to serve.