Heat the oven to 180C/160C fan/gas 4 and line a 35 x 25cm swiss roll tin with non-stick baking parchment. Beat the egg whites in a large bowl using an electric whisk or in a stand mixer until frothy and just holding their shape. Add half of the light brown soft sugar, 1 tbsp at a time, until the peaks turn glossy and firm up. Set the bowl aside.

Beat the yolks with the remaining brown sugar in a clean bowl using an electric whisk or in a stand mixer for 3 mins until pale and fluffy. Sift in the cocoa and a pinch of salt, then fold together to combine. Beat in a third of the egg white mixture to loosen, then gently fold in the rest of the egg white mixture until you have a light batter. Pour this into the prepared tin, spread out to the edges using a palette knife and bake for 12-15 mins until a skewer inserted into the middle comes out clean.

Sprinkle caster sugar over a large sheet of baking parchment. Turn the sponge out onto the sugared parchment, then peel off the sheet that lined the tin. Cover with a clean tea towel, then leave to cool fully.

While the sponge cools, make the decoration. Spoon 2 tbsp of the melted caramel chocolate over a sheet of baking parchment and spread it into a 10cm circle using the back of the spoon. This will be the reindeer face. Arrange the two pretzel halves at the top to make antlers. Spoon 1 tsp of the melted chocolate onto the parchment and spread into a small circle, then repeat three times (these will be the hooves). Chill for 10 mins to set.

Trim the edges of the cooled sponge, then with one of the shorter ends closest to you, score along the inside edge using a sharp knife. Roll the sponge up from the scored edge, using the parchment to make it easier, then unroll and set aside.

To make the buttercream, tip the butter, icing sugar and cocoa into a large bowl and beat with an electric whisk for 4-5 mins until smooth and creamy. Or, do this in a stand mixer. Add 2-4 tbsp boiling water from the kettle and whisk until the mixture is soft but still holds its shape. Spread a thin, even layer over the sponge, then carefully roll it back up.

Spoon the remaining buttercream into a piping bag with a ‘grass’-style nozzle – that’s one with many small holes in it that will create a ‘furry’ texture. Place the rolled sponge on a serving plate or cake stand. Pipe the buttercream all over the outside of the roll, except the front. Squeeze as you start to pipe, then slowly lift the nozzle away for longer strands.

Roll a marble-sized piece of red fondant and attach to the middle of the face using buttercream. Roll two pea-sized pieces of black fondant into small boomerang shapes for closed eyes and attach these above the nose with more buttercream.

Arrange the chocolate hooves on either side of the roll. Pipe a little buttercream on the front of the roll, then attach the face. Will keep in an airtight container for three days.