Put the cranberries and grapefruit zest in a jar, then pour pomegranate juice over them. Mash everything together with a pestle or the back of a large spoon. Cover and let sit for a few hours or overnight. Add the sugar and heat everything in a saucepan over low heat until it begins to thicken. Let cool and add vodka. Strain through cheesecloth, then twice through a single coffee filter. Strain one more time through 2 filters. Bottle and refrigerate. Keep cold until serving. This one is delicious topped with ginger beer. A drink with spirit, ginger and citrus is usually called a “Mule,” but I call this winter Mule a “Reindeer.”