For the batter, beat the eggs, egg yolks, sugar, salt and lemon zest until frothy. Melt the butter and let cool until lukewarm. Gradually stir the butter into the egg mixture. Sift the flour and cornstarch and mix together. Slowly fold into the egg mixture.
Peel, halve and core the pears. Pour half of the batter into a lined springform pan and arrange the pear halves in a star shape on top of the batter. Pour in the remaining batter and smooth. Bake for 45-50 minutes at 190°C (approximately 375°F), until a toothpick inserted into the center comes out clean. Allow to cool and remove from the pan.
For the decoration, melt the chocolate. Pour the chocolate into a pastry bag and use to decorate the surface of the cake. Whip the cream and mix with the cocoa powder. Decorate the cake with cream rosettes. Garnish with chocolate curls and serve.