Instructions

1. Preheat the oven to 180oC (fan 160oC/350oF/Gas 4). Lightly grease the Swiss roll tin with butter and line with baking parchment. It helps to make a small diagonal snip in each corner of the baking parchment, about 3cm (11⁄4in) long, so the paper fits snugly into the corners of the tin.
2. Break the chocolate into pieces and place in a heatproof bowl set over a pan of gently simmering water. The base of the bowl must not touch the water. Leave until just melted, then remove from the heat, stir, and leave the chocolate to cool slightly (see p278, Make a light cake, step 1).
3. Meanwhile, place the egg whites in a large bowl and whisk using an electric hand whisk on high speed until fluffy and stiff, but not dry.
4. Tip the caster sugar and egg yolks into another large bowl and whisk on high speed until light, thick and creamy for about 11/2 minutes. Pour in the cooled chocolate and stir until blended. Add two large spoonfuls of the egg whites to the chocolate mixture and mix gently, then fold in the remaining egg whites. Sift the cocoa and fold it into the mixture. Pour the mixture into the prepared tin and level the surface (see p278, Make a light cake, step 2).
5. Bake for 20–25 minutes or until the cake is well risen and firm on top. Remove the cake from the oven and set aside, leaving it in its tin, until cold (expect it to dip and crack a little).
6. Place the cream in a bowl with the Baileys Irish Cream liqueur and whip until thick enough to just hold its shape. If insufficiently whipped it will be too runny to spread; if over-whipped, it will become too thick to spread evenly.
7. Lightly dust a large piece of baking parchment with icing sugar. Turn the cake out onto the parchment and carefully peel off the lining paper. Spread the surface of the cake with the whipped cream, leaving a bare rim of about 2cm (3⁄4in) all the way around the edges. With one of the short ends near you, make a score mark 2cm (3⁄4in) in from this edge, being careful not to cut right through. Starting at this point, tightly roll up the roulade. Transfer the roulade to a serving platter or board. (See pp278–79, Roll a neat roulade.)
8. Make the icing: put the icing sugar in a bowl, then mix in the cream and enough Baileys Irish Cream liqueur to give a smooth consistency. Drizzle the icing over the top of the roulade, or pipe it using the small piping bag.