300ml double or whipping cream, whipped until thick
White chocolate curls (optional)
Lightly butter a deep 23cm round cake tin and line the bottom of the tin with baking parchment.
Put the eggs and sugar into a large bowl and whisk together with an electric mixer on high speed until the mixture is pale and thick enough to leave a trail on itself when the whisk is lifted out.
Sift together the flour, cocoa powder, and cornflour, and fold half into the egg mixture. Pour half of the cooled butter around the edge; fold in gently.
Repeat with the remaining flour mixture and butter, folding gently.
Turn the mixture into the prepared cake tin and tilt the tin to level the surface. Bake in a preheated oven at 180°C/gas mark 4 for 35–40 minutes until the sponge is well risen and firm to the touch. Turn out on to a rack, peel off the lining, and cool.
Cut the cake in half horizontally and sandwich the layers together with half of the whipped cream. Cover the cake with a thin layer of cream, then pipe the remainder around the top and bottom edges.
Press the chocolate curls over the top and side of the cake, if preferred.