Print the Halloween pattern template on an A4 piece of paper and place in a Swiss roll tin, then put a piece of baking paper over the template. 

Preheat oven to 190C / 180C  Fan / Gas Mark 5 and line a 23 x 23cm tin with non-stick parchment paper. 

For the Halloween batter, in a bowl sieve together the plain flour and the icing sugar. 

Add the egg white and melted butter and mix together until smooth. 

Put two tablespoons of the mixture into a small bowl, add in a few drops of black food colouring. Then add two tablespoons of mixture into another bowl adding in a few drops of orange food colouring. In another bowl add 1 tablespoon of mixture with red food colouring and finally add green food colouring to the remaining mixture. Stir each bowl well, then fill the piping bags with each colour and cut off the tip. 

Carefully pipe the Halloween pattern onto the baking paper, using the coloured template as a guide. Put it into the freezer for 10 minutes and then remove the A4 paper underneath. 

For the sponge, put the eggs, egg yolk, caster sugar, cream of tartar and vanilla extract into a large mixing bowl. Use an electric mixer and whisk until it is pale, fluffy and thickened. 

Sieve together the flour and the baking powder. Add in 1/3 of the flour at a time and very gently fold into the egg mixture. 

Remove the Swiss roll tin from the freezer and pour the mixture over the Halloween pattern. Gently spread out. 

Bake for about 8-10 minutes. It should be golden brown in colour and feel firm and springy to the touch when it is cooked. Remove from the oven and place onto a wire rack. 

While the sponge is still hot, place a large piece of baking paper over the sponge. Then put a large tray over the baking paper. Flip the cake over, remove the swiss roll tin to reveal the baked Halloween pattern. Very gently peel off the baking paper. 

Put another large piece of baking paper on top of the Halloween pattern and another tray on top. Turn the cake over again so the Halloween pattern is facing down. Remove the first piece of baking paper. 

While the sponge is still warm, begin rolling the sponge using the baking paper to help, and rolling it away from you, so the Halloween pattern is on the outside. Roll up tightly, then leave on a wire rack to cool. 

Once cool, carefully unroll the sponge. Spread the chocolate buttercream icing all over the sponge and sprinkle with white chocolate chunks before rolling the sponge up. 

Place the Halloween Patterned roll on a serving plate or board. Leave in the fridge for 30 minutes before slicing. Enjoy!