Sift the flour and cocoa powder into a bowl. Make a well in the centre and whisk in the beaten eggs. Gradually whisk in milk, melted butter and sugar. For best results, set the pancake batter aside for 20 minutes to rest.
Heat a heavy-based non-stick frying pan (about 20-22cm in diameter) over moderate heat. Use a piece of kitchen paper to grease the pan with a little sunflower oil.
Use a soup ladle to pour some batter into the middle of the pan, just enough to create a slightly thicker pancake than a crepe. Cook for a minute or so until the pancake edges start to crisp up. Use a palette knife to flip the pancake and cook the other side, about 1 minute. Turn out of the pan and repeat with remaining batter, greasing the pan between pancakes if necessary.
Stack the pancakes on top of each other to keep warm.
Cooked pancakes freeze (and thaw) very well so don't be afraid to cook a double batch. Interleave leftover pancakes with greaseproof paper and freeze in a food zipper bag.