In the comments on my guacomole recipe, Juti (thanks, Juti!) provided a link to this recipe for an avocado milkshilk on this very cool blog, the Traveler's Lunchbox, written by a gastronome named Melissa.
I just tried the recipe. I can't decide whether it is more aptly described as "heavenly" or "obscenely delicious."
It was also ridiculously easy.
I'm posting the recipe here the way I made it, because I want easy access to it. But you should follow the links and read Melissa's essay about "the secret life of avocados" and check out the rest of her entries as well.
Holly's ever-so-slightly-modified Avocado Milkshake
1 ripe Haas (dark-skinned) avocado, peeled and pitted
1/3 cup sweetened condensed milk
1 cup cold milk, more or less depending on thickness desired
several handfuls of ice
a splash of amaretto (Melissa recommends a few drops orange extract, or some vanilla, rum or coffee, but as I didn't have rum or orange extract or brewed coffee and wanted something more exotic than vanilla, I tried a substitution, which worked OK)
Put everything in a blender and blend on high until the ice is chopped fine. Pour in a glass and enjoy.