Budapestbakelse

Instructions

1. Preheat the oven to 180 °C and line a 20 cm square tin with baking paper.
2. Whisk the eggs with the sugar until pale and foamy, about 5 minutes.
3. Mix the flour, potato starch and baking powder, then gently fold them into the egg mixture with a spatula.
4. Pour the batter into the tin and bake for 12 to 15 minutes, until the sponge springs back when touched. Let it cool.
5. For the custard, heat the milk with the scraped vanilla, then thicken with the cornflour, sugar and a beaten egg yolk until it sets. Add the butter at the end and let it cool.
6. Split the sponge in half horizontally, spread one half with jam and then custard, and top with the second half.
7. Melt the chocolate with the butter in a bain-marie and spread it over the top of the cake. Chill for an hour before cutting.