Preheat the oven to 180°C, fan 160°C, gas 4. Prepare and grease 2 x 20cm round cake tins, lining each base with greaseproof paper.
To make the sponge, cream the egg yolks with the sugar until pale and creamy.
Whisk the egg whites to soft peaks and fold into the yolk and sugar mixture, along with the ground hazelnuts, flour, baking powder, poppy seeds and lemon curd.
Divide the mixture between the tins and bake for 20 minutes until it springs back. Meanwhile, make the cream. Blend the ricotta with the lemon curd and chill in the fridge for 2 hours until the cake has cooled.
Remove the cakes from the tins once cooled. Spread with half the ricotta mixture then sandwich together and spread the remaining mixture on top. Sprinkle with lemon zest to decorate.
Cook's tip: poppy seeds are great store cupboard baking standbys. Sprinkle them over sausage rolls and pies before baking, or add a handful to citrus cake and muffin mixes.