Sift the flour, cocoa powder, baking powder, salt and sugar into a large mixing bowl. Whisk together the eggs and milk in a jug then pour half onto the dry ingredients, whisking simultaneously until you have a smooth, thick batter. Pour the remaining milk and egg mixture into the batter, whisking as you do until you have a smooth batter. Transfer the batter to a large just and cover, allowing it to rest for at least 30 minutes.
When ready to cook the pancakes, whisk the batter to loosen it. Heat tablespoons of the melted butter in a non-stick frying pan and cook the batter until it sets on the bottom. Flip them and cook the other side until set; the centre should be slightly soft so take care to not overcook them. Keep warm on a plate lined with aluminium foil that can cover them loosely. When ready to serve, arrange them stacked on a plate with nonstick baking paper squares dividing them.