Lime Kefir Frozen Yogurt

My lovely siblings gave me an ice cream maker for Christmas! Another opportunity for scheming. I'm not an experienced ice cream maker, and in fact unsuccessfully attempted an ice cream recipe twice in October, so I feel like I need to work up to making actual ice cream. I made this lemon kefir ice cream a few years ago, and very much liked it.

It is the simplest of frozen dessert recipes: mix, refrigerate, mix, freeze - no cooking required. And it's probably the healthiest of frozen desserts, since it's low-fat and only sweetened by agave syrup.

Lime Kefir Frozen Yogurt

1 2/3 cups kefir (or other fermented milk, or buttermilk, or plain yogurt; low fat makes it icier)
the zest from two limes, microplaned or very finely chopped
1/4 cup lime juice (a little less than the yield of the 2 zested limes)
1/3 cup plus 2 tablespoons agave syrup (or the sweetener of your choice -- maple syrup, rice syrup, honey, or a mix of honey and sugar)
a good splash of rum (or lemoncello, or cachaça) (optional)

Makes about 1/2 liter (1/2 quart).

Combine all the ingredients in a mixing bowl and whisk until blended. Cover, refrigerate for an hour until well chilled, and churn in your ice cream maker according to the manufacturer's instructions. Let it firm up in the freezer in a plastic container; mine took about a day to be firm enough to form scoops, since the mixture is low in fat and my freezer is not the coldest. Has an icy, sorbet-feel to it.