- Whisk the eggs and sugar: Preheat the oven to 220°C (200°C fan oven), gas 7 and cover a large baking sheet with a sheet of baking parchment. In a large mixing bowl use an electric mixer to whisk the eggs with half the caster sugar until pale and very thick; the mixture will hold its shape. This takes about 3 minutes on high speed.
- Add the flour: Sift the flour and 2 tbsp cocoa evenly over the mixture, then use a large metal spoon to fold it in, turning the mixture over in big scoops rather than stirring it.
- Bake the sponge: Pour the mixture on to the parchment and spread it out lightly into a rectangle about 23 x 33cm. (Do not press heavily – it does not matter if the edges are not quite square.) Bake for 8-10 minutes or until risen, set and springy in the middle.
- Make the syrup: While the sponge is baking, put the remaining caster sugar into a pan with 2 tbsp of the remaining cocoa and 150ml water. Bring to the boil, stirring, and boil for 2 minutes. Remove from the heat and stir in the brandy, vanilla extract and butter. Set aside over a low heat to keep warm.
- Turn out the sponge: Dampen a clean tea towel with hot water, then lay it on a clean surface. Lay a sheet of baking parchment on top and sift the remaining cocoa and the icing sugar over to about the size of the sponge. Take the sponge from the oven and invert it on to the cocoa on the paper.
- Roll the sponge: Peel off the lining paper and trim off the crisp edges. Make a shallow cut about 1cm in from a long edge but not right through the sponge. Dollop the chocolate spread over the sponge and spread it out thickly – no need to be too fussy. Roll up the sponge and filling from the long edge with the cut, using the cut to start the roll tightly. Hold the paper and damp cloth to guide the roll, then hold the roll firmly in the damp cloth for a minute, so that it sets in place.
- Serve: Take off the towel and paper, sprinkling the cocoa mixture over the sponge. Don't worry if the roll is slightly cracked. Cut six slices of roll, using a serrated knife, and arrange them on serving plates, then spoon the hot syrup over the top.
For an alcohol-free version, omit the brandy.
Raspberry sponge pudding: Make the sponge without the cocoa. Sprinkle 300g frozen raspberries over the sponge just before putting it in the oven. Bake for 10-15 minutes. Heat 6 tbsp raspberry jam with 6 tbsp dry sherry or cider, or apple juice, until melted. Serve the hot sponge cut into squares, overlapping two squares on each plate. Drizzle the raspberry sauce over and serve with cream or ice cream.