While the donut holes are cooling, make the glaze. In a small bowl, place the confectioners’ sugar and 1 tablespoon of milk. Mix well, until a thick paste forms. Add more milk by the 1/4-teaspoon, mixing to combine well, until the glaze falls off the spoon slowly, in a thick but pourable glaze. Add milk very slowly, as it is much easier to thin, than to thicken, the glaze. If you do thin the glaze too much, add more confectioners’ sugar a teaspoon at a time to thicken it. Immerse each cooled donut hole in the glaze and lift out with the tines of a fork or chocolate dipping tool, and return to the wire rack for any excess glaze to drip off. Allow the glaze to set at room temperature and serve immediately.