To make ahead:Make the cupcakes 1-2 days in advance (making them up to step 8 of the recipe) and store them, covered, in the refrigerator. (Do not poke holes in them yet).
To freeze: Make cupcakes up to step 8 and allow them to cool completely. Do not poke holes in them yet. Store them in a freezer safe bag for 2-3 months. Allow them to thaw completely, then poke holes and pour milk mixture over them.
Recipe adapted from Tres Leches Cake from the Pioneer Woman.