The eggs should be at room temperature so take them out of the fridge an hour before using them.
Melt the butter over a low heat and leave it to cool.
Crush the red peppercorns in a mortar and pestle as best you can. Mix the flour with the ground pepper.
Put the eggs, sugar, and a pinch of salt in a mixer bowl. Mix until the eggs turn white and triple in volume (at least) – about 10 minutes.
Slowly add the melted butter and lemon curd. Mix for 1 more minute.
Gently fold in the flour, using upward movements. Make sure to keep as much volume as possible.
Preheat the oven to 180 °C (360 °F). Line a 30/40 cm (12x16 inch) baking tray with parchment paper. Pour the mixture into the tray, level it, and place in the preheated oven. Bake for 15-16 minutes, until lightly browned.
Remove the tray from the oven and flip the sponge onto a towel sprinkled with icing sugar. Using the towel to help, roll the sponge up while still warm. Leave it to cool.
When completely cool, carefully uncover and unroll it. Spread the lemon cream evenly, leaving a margin of about 2 cm (3/4 of an inch) at the edges. Roll the cake up as tightly as possible. Transfer to a platter.