Warm your oven to 180°C/Fan 160°C/Gas 4. Fill and boil your kettle. Pour enough boiling water into a small pan to fill it by a third. Pop the pan on the hob, set to the lowest heat setting. Line the base of your largest baking tray or roasting tin with greaseproof paper.

Break 100g of the chocolate into small pieces and slide it into a heatproof bowl. Place the bowl on top of the pan of hot water (making sure that the bottom of the bowl is not touching the water). Turn off the heat and stir the chocolate occasionally for 3-4 mins, till melted and smooth. Once melted, pop the bowl to one side to cool.

Separate 5 egg yolks and whites into two large, clean, grease-free bowls. Whisk the egg whites until they form stiff peaks, then set the bowl to one side. Measure out 100g of the sugar and pour it into the bowl with the egg yolks. Grate in the clementine zest. Whisk the yolks, sugar and zest together for 3-4 mins, till the mixture is smooth, thick and light in colour.

Pour 3 tbsp double cream into a small bowl and squeeze in the juice from 1 clementine. Stir to combine, then stir the cream and juice into the bowl with the yolks and sugar. Stir in the cooled, melted chocolate.

Tip the flour into a small bowl and mix in the baking powder. Tip the flour and baking powder into the bowl with the chocolate mixture and fold till combined. Add half of the whisked egg whites and stir in to loosen the mixture. Carefully fold in the remaining egg whites till combined. Pour the batter onto the lined baking tray and spread out into a thin, even layer. Slide the tray into the oven and bake for 10 mins, till the sponge is light and set.

When the sponge is cooked, let it cool down slightly till just warm enough to handle. Slide the sponge and greaseproof paper off the baking tray onto a worktop. Starting with the narrowest end, roll the sponge and greaseproof paper tightly into a cylinder. Pop the cylinder onto a wire wrack and allow to cool.

While the sponge is cooling, make the chocolate ganache for covering the yule log. Pour 200ml double cream into a small pan and warm till just simmering. Break the remaining 100g chocolate into a heatproof bowl. When the cream is hot, pour it over the chocolate and use a wooden spoon to stir together into a smooth and thick sauce. Once combined, cover the bowl with a plate and pop in the fridge for 20 mins to thicken.

When the sponge has cooled, pour the remaining cream into a large bowl. Add the remaining sugar and whisk till it just forms soft peaks. Carefully unroll the sponge (it is absolutely fine if it cracks or breaks in places, just keep the pieces together). Spread the cream evenly over the sponge, leaving a 1cm-thick edge. Carefully roll the sponge and cream back up, as tightly as possible, and transfer the sponge to a serving plate or board.

Spoon the thick, cooled ganache over the rolled up sponge and spread evenly all over the sides and ends, making sure to patch up any cracks or breaks in the sponge. Serve the yule log sliced into generous rounds.