Melt the butter and leave to cool slightly. Beat the eggs, sugar and salt until frothy. Mix the flour with the baking powder and bicarbonate of soda, then add to the egg mixture together with the syrup and mild fruity verjuice and mix thoroughly. Place the batter in the fridge for 1-2 hours and leave to rest. Fill the madeleine tin with 3/4 of the batter and bake in a preheated oven at 180°C top/bottom heat for approx. 12 minutes. Then decorate as desired.