1. Preheat the oven to 350°F (180°C). Line a 15½ × 10½ × 1in (39 × 27 × 2.5cm) jelly roll pan with wax paper.

2. Beat the eggs and sugar in a large bowl with an electric mixer at high speed about 5 minutes, until the mixture has tripled in volume. Sift the flour, cocoa, and baking powder together. Sift over the egg mixture and carefully fold together.

3. Spread in the pan. Bake about 15 minutes, until the top springs back when pressed lightly with a finger. Sift confectioner's sugar over the cake. Place a clean kitchen towel and a cutting board over the jelly roll pan. Invert them together to unmold the cake. Remove the wax paper and place on the cake. Roll up the cake, with the paper inside. Let cool.

4. Meanwhile, to make the icing, bring the cream to a boil in a small saucepan. Add the chocolate and stir until melted. Remove from the heat and let cool for 10 minutes.

5. Unroll the cake and discard the paper. Spread the preserves over the cake. Roll up the cake again. Place the roll on a wire rack, seam side down. Spread the icing all over the top, sides, and ends of the cake. Use a fork to create ridges down the length of the cake. Transfer to a platter. Just before serving, dust with confectioner's sugar.