Preheat the oven to 350 degrees F. Spray a donut pan with non-stick spray. Set aside.
Mix together the milk, sour cream, and egg together until smooth.
Add melted butter and vanilla, mixing until combined.
Add flour, baking powder, baking soda, nutmeg and sugar. Stir until just combined. Do not over-mix. The batter will be thick.
Fold in the sprinkles gently so they won't bleed.
Spoon the batter into the donut pan. It is easiest if you use a large zipped-top bag and cut a corner off the bottom of the bag and pipe the batter into each donut cup, filling 3 ∕ 4 of the way full.
Bake for 9–10 minutes or until the edges are lightly browned. Remove from pan and allow the donuts to slightly cool before glazing. The glaze sets easier onto cooled donuts.
To Make Glaze:
Mix together the glaze ingredients in a medium saucepan over low heat. Whisk until the glaze is smooth.
Remove from heat and quickly begin dipping the donuts, one by one, into the glaze. Place each donut on a wire rack over a baking sheet to catch the glaze drippings. Take each donut and dunk again if you have enough glaze leftover. Sprinkle with additional sprinkles.