Heat the oven to 180°C / 160°C fan. Line a 33x23cm Swiss roll tin with baking paper.

Whisk the yolks with 100g of the sugar for 4 minutes until pale and thick enough to leave a ribbon, then fold in the cocoa and vanilla.

Whisk the whites with the salt to soft peaks, add the remaining 50g sugar and whisk to firm, glossy peaks.

Fold a third of the whites into the chocolate mixture to loosen it, then fold in the rest in two goes, stopping while a few streaks remain. Overfolding here is why roulades crack.

Spread into the tin and bake 18–20 minutes until risen and springy. Cover with a damp tea towel and cool completely in the tin; the damp cloth keeps it flexible.

Whip the cream with the icing sugar, orange zest and Cointreau to soft peaks.

Turn the sponge out onto baking paper dusted with cocoa, spread the orange cream over, and roll firmly from a short edge using the paper to help. A few cracks along the top are correct, not a failure.

Make the ganache. Pour hot cream over the chocolate, wait 2 minutes, stir from the centre until glossy, then beat in the butter. Cool until spreadable.

Cover the log, drag a fork along it to make bark, and finish with icing sugar snow, rosemary and cranberries.