Preheat the oven to 350°F and spray donut pans with nonstick spray.
In a big bowl, whisk together melted butter, both granulated and light brown sugar, vanilla extract, sour cream, and egg.
Once mixed, add all the dry ingredients and whisk until just combined. Pour in the milk and whisk until smooth.
Fill a large piping bag with the batter or use a spoon to scoop it into each pan, filling each donut ⅔ of the way.
Bake for 12-15 minutes until golden brown and cooked through. Let them cool for 5 minutes before transferring to a cookie rack to cool completely.