To make the pancakes, sift the flour and cocoa into a bowl, add the egg and egg yolk, 1 tablespoon of the oil then gradually whisk in the milk until smooth. Leave to stand for 15 minutes.
For the filling, mix the yogurt, custard and chopped mint together. Mix the berries together in a separate bowl. Melt the chocolate if using to decorate, in a bowl set over a small saucepan of gently simmering water.
To cook the pancakes, heat a little oil in the base of an 18 cm (7 inch), pour the excess out of the pan into a bowl then add 2-3 tablespoons of the pancake batter to the pan, tilt pan to swirl the batter over the base in a thin layer then cook until browned on the underside. Turn the pancake over and cook the second side then slide out of pan and keep hot on a plate while you cook the remaining mixture until you have 8 pancakes.
Fold the pancakes into quarters, spoon in the yogurt mix and berries, arrange in pairs on serving plates and drizzle with melted chocolate, if using. Serve immediately.
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