Grease your pan. Add a thin layer of bread crumbs.
Crack your eggs in one of the glasses. Pour an equal amount of sugar into the next one. Measure 70% of wheat flour in the third glass and fill the rest with potato starch.
Whisk the eggs and sugar to white and fluffy. This takes at least 7 minutes. Whip with a lower speed and increase to the middle speed.
Sieve the flour and gently turn them into foam. Mix very gently into an even batter.
Pour your batter into the greased pan. Bake at 350 F for 35 minutes on the lower rack in the oven.
Test your cake is done with a toothpick. If it comes out clean you can take your cake out. Drop the cake from one foot high directly hot from the oven. This makes air tunnels and you don´t get a sunken middle.
Notes
Use this sponge cake to make a layer cake with fresh berries and whipped cream or eat as it is with vanilla custard.