- Preheat the oven to 325°F (160°C). Line the bottom of a 9-inch (23 cm) springform pan with parchment paper, but do not grease the pan or line the sides with parchment.
- Using beaters or a stand mixer fitted with a whisk attachment, whip the eggs and sugar on high speed until they are almost white in colour, more than triple in volume and hold a ribbon when the beaters are lifted, about 5 minutes.
- Sift the flour and salt and, still on medium speed, add the flour to the egg mixture. Spoon about a cup of the batter into a bowl, and stir in the melted butter and vanilla. Add this all back to the full batter and stir by hand until blended. Pour the batter into the prepared pan and bake for about 40 minutes, until the centre of the cake springs back when gently pressed. Cool the cake completely in the pan.
- To extract the cake from the pan, run a palette knife around the inside edge of the pan to loosen to cake, then unlatch the ring and peel away the parchment paper from the bottom.
Genoise sponge can be made a day ahead and wrapped in plastic wrap (do not refrigerate), or frozen and thawed when needed.