Preheat the oven to 350. Next, grease your donut pan.
Melt the butter and set aside.
Stir together flour, sugar, salt, and baking powder in a large bowl.
In a separate medium bowl, mix together melted butter, egg, sourdough starter and water.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to over mix.
Scoop the batter into a piping bag or zip-lock bag and clip the corner about 1/4-1/2 inch wide.
Squeeze the batter into each donut well.
Place in the preheated oven and bake for 15-17 minutes.
Pop donuts out of the pan and place on a wire rack to cool.
In a medium bowl, whisk together powdered sugar, vanilla extract, and milk or cream.
Gently place the donuts in the glaze on one side, pick up and place the non-glaze side down on a cooling rack.
Sprinkle some sprinkles on top if desired.
Notes
To prevent dense donuts and get a nice and light texture, I suggest pouring the flour (or using a spoon to scoop) into the measuring cup and then leveling it off. Rather than scooping the flour right out of the bag.
Place the batter in a pastry bag or zip-lock bag to easily pour into a donut pan.
Don’t have a donut pan? You can also use a muffin tin and add a small ball of aluminum foil in the middle.
The tops of the donuts will not get very golden, making you question if they are truly done, but they probably are. If you gently press the donut it should spring back a bit and the bottoms will be golden.
Be careful not to over bake.
Don’t overfill the pan. There should be enough batter to perfectly fill 12 donuts.