“Don't be daunted by the length of the recipe or the rolling – this tropical roulade is surprisingly uncomplicated. And whether it's for a celebration or an afternoon-tea treat, it'll definitely impress. ”
Start by making the filling. Finely chop the chocolate and place in a heatproof bowl. Heat the coconut cream in a small pan until hot but not quite boiling, then pour it over the chocolate.
Finely grate over the lime zest, reserving a little for garnish, then leave to stand for 1 minute. Whisk together until smooth, then cover and pop in the fridge while you get on with the sponge.
Preheat the oven to 180ºC/350ºF/gas 4. Grease a 37 x 26.5cm baking tray with the unsalted butter and line the base with greaseproof paper.
In a mixing bowl, whisk together the plain flour, desiccated coconut, 175g of granulated sugar, the baking powder, bicarb of soda and 1 good pinch of sea salt.
In a larger mixing bowl, whisk together 3 egg yolks (reserving the whites), the oil and coconut milk until combined. Add half of the dry mix to the bowl and stir, then add the remaining mixture and stir until smooth and combined.
Place the 5 egg whites in a large mixing bowl (reserving the yolks for another recipe) and whisk on a medium speed with an electric whisk or a free-standing mixer until soft peaks form. Increase the speed and gradually add 75g of the remaining sugar until you have glossy stiff peaks.
Add a large spoonful of the whisked egg whites into the cake mixture and fold through with a metal spoon. Add the remaining whisked egg whites and fold, so it’s still light and airy.
Spoon the batter into the prepared baking tray and bake for 16 to 18 minutes, or until golden and cooked through.
Cut a piece of greaseproof paper, a good 10cm larger than the sponge, and sift with the icing sugar. Carefully loosen the edge of the cake and turn it out onto the paper. Peel off the top piece of greaseproof paper and leave to cool for 5 to 10 minutes.
Starting lengthways, roll the sponge up like a swiss roll, using the greaseproof paper as a guide. While the sponge cools completely, make the syrup.
Squeeze the juice from the limes into a small pan and add the final 50g of granulated sugar. Place over a medium heat, gently bring to the boil, then reduce the heat and simmer until you have a light syrup. Leave to one side to cool.
To put the roulade together, remove the white chocolate mixture from the fridge and whisk until thickened and smooth.
Unroll the sponge, and drizzle over the lime syrup. Spread over the thickened white chocolate mixture, leaving a slight border around the edge, then roll up again lengthways, using the greaseproof paper as an aid. Set it on a platter and pop in the fridge until you are ready to serve.
Finish by dusting with a little more icing sugar, and sprinkle with lime zest and toasted coconut flakes, if you like.