Preheat oven to 180 degrees C. Line baking tray with baking paper.
In a mixing bowl beat sugar, vanilla, lemon zest and 6 tablespoons of butter with an electric mixer until well blended.
Add eggs one at a time, beating well after each addition. Continue to beat for 1 minute.
Stir in flour and baking powder (will be a soft, sticky dough).
Spoon dough into a pastry bag fitted with a 3/8-inch round tip. Pipe 2cm diameter rings onto the prepared baking tray.
With moistened fingertips press ends of each ring together to form a smooth ring.
Bake about 20 minutes or until golden brown.
Icing: Melt 1 tablespoon of butter over low heat. Add sugar, water, lemon juice and vanilla then whisk until sugar melts and mixture is heated through. Thin with more water if icing is too thick to brush.
Remove biscuits from oven and immediately brush warm icing over hot biscuits.
Cool iced biscuits on baking tray for 2 minutes. Transfer to a cake rack and cool completely.