01 -
Preheat oven to 350°F (175°C). Grease a donut baking pan.
02 -
In a bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon. In another bowl, mix milk, sour cream, egg, vanilla extract, and melted butter. Stir wet ingredients into dry until just combined.
03 -
Spoon or pipe the batter into the donut baking pan, filling each cavity about 2/3 full.
04 -
In a small bowl, mix flour, brown sugar, and cinnamon. Cut in cold butter using a fork or pastry cutter until crumbly. Sprinkle over the donut batter.
05 -
Bake for 10–12 minutes or until the donuts spring back lightly when pressed. Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
06 -
Once the donuts have cooled, drizzle them with a glaze made from powdered sugar and milk, if desired.