For the strawberry sauce thinly slice 400g strawberries and place in a bowl. Sprinkle sugar on top and let rest for 10 minutes. Cut remaining strawberries in quarters and set aside for garnish.
Meanwhile make the pancake batter: sift flour, baking powder and cocoa powder into a big bowl. Add salt and sugar and mix well. Add milk, egg and melted butter and whisk until smooth.
Melt a knob of butter in a non-stick frying pan. Ladle the batter into the pan using about 1/8 of the batter for each pancake. When bubbles start forming on top, flip the pancake over and cook a few more minutes on the other side. Transfer to a plate to keep warm and repeat with the remaining batter.
Mash the sugared strawberries with a fork or puree in a food processor. Serve the pancakes with the strawberry sauce spooned on top and garnish with the strawberry quarters.