Preheat oven to 190°c. Mix butter and sugar until fluffy. Add vanilla and mix. Sift in flour and salt in batches, mixing well between additions. Add the cherries and mix again. Spoon mixture into a piping bag with a 2.5cm star nozzle, and pipe rings onto two nonstick baking sheets. Bake for 8-10 minutes, or until light and golden. Leave to cool on a wire rack.