- Beat the butter and sugars together with an electric whisk until pale and fluffy. Beat in the egg, vanilla and food colouring until you have a bright red batter. Sieve over the flour, cocoa and bicarb. Fold everything together to make a stiff evenly-coloured dough, then fold in the chocolate chips.Put the dough on a sheet of baking parchment, fold the parchment over the dough and mould into a sausage shape about 6cm wide. Chill until ready to bake. Will keep for a week in the fridge or one month in the freezer.
- Heat the oven to 190C/170C fan/gas 5. Cut the cookie dough into 1cm thick slices using a sharp knife and arrange on two large baking sheets lined with baking parchment well-spaced apart so they have room to spread in the oven. Bake in batches, keeping the unbaked cookies on the sheet in the fridge while the rest are baking.
- Bake in the middle of the oven for 13-15 mins until the cookies are crisp at the edges, but still soft in the centre. Leave to cool on the baking sheet for a few minutes, then transfer to a wire rack to cool completely. Beat the soft cheese in a small bowl to a loose consistency, then stir in the icing sugar. Use a piping bag or spoon to drizzle the icing over the cookies.