Good news. You can freeze leftover cosmopolitans. Now, the purest of drinkers may vote against this, but we do it and have never had any qualms about it. Just pour any leftover cosmopolitans into a freezer-safe container. Be sure to add a label with the name of the drink and the date you put it in the freezer. Then, simply, put it in the freezer. When you're ready to drink it, we suggest leaving it at room temperature for a half hour before pouring. For a little bit of the science behind putting alcohol in the freezer, and why vodka won't freeze in the freezer, check out this post.