Sift all the flour onto the egg foam at once. Using the paddle (K) attachment, mix on a low speed, or fold it in very gently and carefully by hand with a spatula, using scooping motions from the bottom up, to keep as much volume in the batter as possible.

Preheat the oven to 150 °C with the fan/convection setting. Line the base of the cake tin with baking paper. Pour the airy batter into the prepared tin and gently smooth the surface. Leave the sides of the tin clean and ungreased.

Bake in the preheated oven for 45–55 minutes. During the first 45 minutes, do not open the oven door under any circumstances, or the sponge will collapse. Once baked, remove it from the oven (test with a skewer or knife) and let it cool in the tin for 5–10 minutes.

Carefully run a thin spatula or knife around the edges of the sponge. Then turn the tin upside down onto a cooling rack and let the sponge cool completely – this helps the surface settle beautifully flat. Peel off the baking paper while the sponge is still slightly warm.

Once completely cool, wrap the sponge tightly in plastic wrap so it doesn't dry out. Let it rest at room temperature (or in the fridge), ideally until the next day. This makes it much easier to slice.

The next day, unwrap the sponge. Using a long, ideally fine-serrated knife, first trim off the thin top crust so the surface is perfectly flat (if you want it flat rather than domed). Then slice the sponge horizontally into as many layers as you need.