Preheat oven to 400F (200C). Stir mix and cocoa in a large bowl. Make a well in centre. Whisk eggs in a small bowl. Stir in milk and vanilla.
Pour into well. Stir until just moistened. Drop by heaping tablespoonfuls onto greased cookie sheets, spacing at least 2 inches (5 cm) apart. If you’re not going to ice, place small candies on top to form a face.
Bake in centre of 400F (200C) oven until edges are brown, from 10 to 12 minutes. Using a large spatula, carefully remove cookies to a rack to cool completely. Store in a sealed container at room temperature for up to 2 days or freeze. Once cookies are cool they can be iced.