Method

• 1.
  Preheat oven to 170°C. Grease 3 baking trays and line with baking paper.
• 2.
  Whisk flour, cocoa, if using, and sugar in a bowl until combined. Rub zest and butter into the dry ingredients with your fingertips until it resembles a coarse dough. Add milk and, using your hands, knead until just combined. Shape into a disc, enclose in plastic wrap and chill for 20 minutes or until firm.
• 3.
  Roll out dough between 2 sheets of baking paper to 4mm thick. Cut shapes with biscuit cutters (we used animal shapes), re-rolling excess dough. Arrange biscuits, 2cm apart, on prepared trays.
• 4.
  Bake biscuits for 12 minutes, swapping top and bottom trays halfway, or until plain biscuits are light golden and chocolate biscuits have darkened at the edges. Remove and set aside to cool for 5 minutes, then transfer to a wire rack to cool completely.
• 5.
  Drizzle melted chocolate over biscuits to serve.