Preheat the oven to 400 F degrees. Lightly grease a couple of baking sheets or silicone mats.
Put the butter and sugar into a large bowl and cream until pale and fluffy. Beat in the egg yolks. Add the rest of the ingredients, except the egg whites, stirring well to make a soft dough.
Put the dough onto a floured surface and knead lightly. Roll out to a thickness of about 1/4 inch. Cut into your preferred shapes and place on the prepared baking sheets. Bake for 5 to 8 minutes.
Meanwhile, lightly beat the egg whites. Brush the cookies with the whites and sprinkle with a little superfine sugar. Return to the oven and bake for a further 4 to 5 minutes, or until golden brown. Cool on a wire rack. Adapted from Sarah Raven's "Fresh from the Garden," published by Universe Books with photos by Jonathan Buckley.