Melt the butter in a small pan, allow to cool slightly. Mix the flour and salt in a bowl, create a well in the middle. Combine the milk, water, eggs and cooled butter, gradually pour into the well while mixing with a whisk, continue to whisk until the batter is smooth. Cover and leave to stand at room temperature for approx. 30 mins.
Cut the rhubarb and strawberries into pieces, place in a pan. Add the sugar and vanilla sugar, mix, cover and simmer over a low heat for approx. 10 mins. until just soft, leave to cool.
Heat a little clarified butter in a non-stick frying pan. Pour enough batter into the pan to thinly cover the base. Reduce the heat. Once the underside is cooked and separates from the pan, turn the crêpe, finish cooking, cover and keep warm. Repeat these steps with the remainder of the batter. Plate up the crêpes with the stewed fruit and yoghurt, dust with icing sugar.