Preheat the oven to 350 degrees F. Mist 2 donut pans with nonstick cooking spray and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt. In a small bowl, whisk together butter, eggs, milk, and vanilla extract. Add the wet ingredients to the dry ingredients and mix until just combined.
Spoon the batter into the donut cavities, filling two-thirds full. Bake for 9-12 minutes or until golden. Remove from the oven and allow to cool for 4-5 minutes before transferring to a wire cooling rack to cool completely.
Meanwhile, mix together all glaze ingredients until smooth, adding food coloring, if desired. Working one at a time, dunk the tops of each donut into the glaze, gently shaking and rotating the donut to limit dripping as you return it to the cooling rack. Decorate with sprinkles, if desired. Best if served within 30 minutes. Leftovers may be stored in the fridge for 3 days.