Has anyone figured out how to incorporate booze into [frozen desserts]? I know it's a problem because the alcohol doesn't freeze but seems to me that I read a recipe once upon a time.
It depends on how much booze you want to add. In this recipe for example (Blueberry Peach Tequila Popsicles, Food & Wine), only 3 tablespoons of tequila are used. The freezing process takes a while, because of the layers.
Alcohol freezes at -173° F (water's freezing point is 32° F), and there's no way your freezer will go that low. So, you have to do something else to get the booze to freeze. I have two suggestions:
The less you use, the closer your mixture will get to being more like water, and thus freezing more easily, so you can try just using a few tablespoons of alcohol in your recipe, instead of, say, half a cup.
You can also try cooking out the alcohol. So if you're going to use rum, for example, simmer the rum over medium-low heat for a few minutes. This will remove the alcohol, but preserve the taste of the rum. If you're making popsicles with booze for the boozing effects, this second solution is probably not what you're looking for.