This light as a feather sponge is made with just three ingredients - potato starch, eggs and sugar. It's based on Pellegrino Artusi's 1891 recipe for "Torta Margherita" (daisy cake), a classic Italian "breakfast cake". It's a great recipe when you need a sponge for other dessert recipes like trifle or Sicilian cassata as it is light, fluffy and dry (so it's wonderfully absorbent for desserts that need a sponge to soak up other flavours and wet fillings). I also use this sponge recipe as is, or filled with freshly whipped cream and strawberries. —Emiko
Beat together the yolks and half the sugar until extremely pale and creamy, about 10 minutes. The longer you beat, the fluffier the cake.
In a separate bowl, beat the whites until fluffy then add the rest of the sugar and continue beating until stiff peaks form. Gently fold some of the potato starch into the yolk mixture, then some of the whites, and continue alternating this way until you have a well-combined, smooth, fluffy batter.
Pour into a cake tin lined with parchment and bake at 350ºF for about 25 minutes or until golden brown and puffed. A skewer inserted in the middle should come out clean. Remove from the oven and let cool slightly in the pan before removing to a rack to cool.