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Heat oven to 190C/fan 170C/gas 5. Butter a large (approx 30cm x 40cm) Swiss roll tin and line the base and sides with baking parchment. Lightly butter the parchment, dust with the plain flour and tip out any excess.
Sift the self-raising flour, baking powder and cocoa into a bowl and mix in the ground almonds. Put the eggs and caster sugar in a large mixing bowl and beat, using an electric hand-whisk or tabletop mixer, for 5-10 mins until pale, thick and trebled in volume. The mixture should leave a trail when the beaters are lifted out.
Fold the dry ingredients into the egg mixture using a large metal spoon. Pour into the prepared tin, then tip the tin from side to side until it is covered in an even layer of batter and the corners are filled. Bake on the middle shelf of the oven for 12-15 mins or until firm to the touch. Meanwhile, lay a sheet of baking parchment on the work surface and sprinkle with caster sugar.
Allow the sponge to cool for 1 min before turning out onto the sugared paper. Peel away the backing paper and, with the short side facing you, roll the sponge away from you so that the sugary parchment is rolled inside the roulade. This will help you to fill and roll it later. Set aside until completely cold.
To make the filling, beat the mascarpone with the orange zest. Unroll the sponge, discard the inside paper and evenly spread the mascarpone over, leaving a finger-width border around the edges. Cover with the cranberry sauce. Using the outside baking paper to help, roll the sponge away from you as tightly as possible. Transfer to a serving platter, cover loosely and chill while you prepare the frosting.
For the frosting, melt the chocolate in a heatproof bowl over a pan of just-simmering water, or microwave on High for 2 mins, stirring halfway through. Set aside for about 10 mins until cooled, but still soft.
Meanwhile, beat the butter and icing sugar together until pale and smooth. Pour in the chocolate and stir thoroughly to combine. Set aside for 20 mins to firm up slightly before using a palette knife to cover the roulade in frosting. Mark with a fork to create a log effect. To decorate, arrange the cranberries and bay leaves along the length of the log. Dust with a little icing sugar just before serving. Cut into slices, removing cranberries and bay leaves to serve. The roulade can be made up to a day ahead. Take it out of the fridge at least 30 mins before you want to serve it, to allow the filling and icing to soften.