For the crepes, sort out the blackberries, wash and drain in a sieve. Melt the butter in a small saucepan and brown lightly. Allow to cool slightly.
Mix the egg with flour, salt, sugar, mineral water and warm brown butter until smooth. Heat a frying pan without fat and fry 4 very thin crepes one after the other.
Whip the cream with sugar and vanilla sugar until stiff. Fill the crepes with whipped cream and blackberries, beat together and sprinkle with powdered sugar.