In a bowl, sift flour, baking powder and add salt. In another bowl beat the butter, sugar, icing sugar, vanillin and lemon rind with the electric whisk until everything is very frothy. Now add the egg, reduce the whisk speed and add the flour in three times.
Finish kneading by hand, but without dwelling too much on the operation. Wrap the dough in plastic wrap and let it rest in the fridge for at least an hour.
Roll out the dough on the lightly floured work surface, up to a thickness of 3mm. Cut the biscuits and place them on the baking tray covered with baking paper. Keep in the fridge until the oven reaches a temperature of 170 ° C, then bake for about 8-10 minutes, or until lightly browned. Allow to cool on a rack.
In a small bowl mix the icing sugar with a couple of tablespoons of lemon juice, so as to obtain a thick glaze. Spread it on the biscuits or put it in a sac-a-poche and decorate to taste. Let solidify and store the lemon cookies in a tin box.
Lemon biscuits are crunchy biscuits scented with citrus peel, perfect to serve with tea or for breakfast