with a mixer, cream together the margarine and sugar until smooth and fluffy.
add in the zest and mint, creaming once more to incorporate and evenly distribute throughout the mixture.
slowly sift in the flour and baking powder, and then add the sour cream, mixing just until the dough comes together.
you may have to use your hands to press it into a cohesive ball, but the jey is to stop mixing when you think it's nearly done.
pinch off pieces about the size of walnits, roll them into balls, and then flatten them out slightly on your prepared sheets using the bottom of a glass or the palm of you hand.
place the whole sheet of unbaked cookies in the freezer for 15-20 minutes, until thoroughly chilled, to prevent them from spreading too much
bake 8-10 minutes, or until firm, but still pale and not quite browned around the edges.
to make the glaze, simply whisk the icing sugar, rum and vanilla together until smooth, and drizzle over the cooled cookies.