Preheat the oven to 180°C and grease a baking tray.
1. Beat the caster sugar and brown sugar with the eggs until light and pale. Add the butter and mix well. Add the flour, hot chocolate and vanilla essence and mix to a soft dough.
2. Roll the dough into small balls and place the balls on the baking tray. Flatten them slightly and bake for 8 to 10 minutes. Leave to cool.