In a Large bowl, whisk together the sourdough starter and milk until the starter is fully dissolved.

Add in the egg, sugar, melted butter, and vanilla until everything is well incorporated.

Next, sift in your flour and salt and mix until no lumps remain.

After mixing, cover the dough with a damp cloth and allow it to rest for 30 minutes.

After the rest period, uncover the dough and knead in a stand mixer with a dough hook on medium speed for 12 minutes, or until the dough pulls away from the sides of the bowl. If working without a stand mixer, perform stretch and folds to develop the gluten and strengthen the dough. For instructions on how to stretch and fold click here.

Cover the bowl with a damp cloth and allow the dough to rise overnight for 8-10 hours at 70°F(21°C). This will take more or less time depending on the temperature of your home. When the dough is ready it will be light, airy, and have doubled in size.

Turn the dough out onto a well floured surface. Use a rolling pin to roll the dough into ½" thickness. If the dough resists being rolled, allow it to relax for 10 minutes and try again.

Use a 2 ¾" biscuit cutter to cut out the donuts. Gather and scraps and allow them to rest for 30 minutes. This will allow you to re-roll the dough and cut more donuts.

Take a cut donut and pierce the center with a chopstick or skewer. Spin the dough around the chopstick until the center hole has stretched to a 1" width. Alternatively, pierce a hole and use your fingers to stretch the dough and form a donut shape.

Place the donuts on a parchment lined surface 2" apart and cover them with a damp cloth. Allow the donuts to rise at room temperature for about 2 hours, or until they have risen by 50% of their original size. See below tip for speeding up second rise.

After the donuts have risen, preheat the oven to 350°F(180°C). Transfer the parchment paper and donuts onto a large baking sheet. Bake on the center of the oven for 13-15 minutes.

Heat 1" of coconut oil in a deep sided frying pan over medium heat until it reaches 350°F(180°C). The amount of oil needed will vary based on the size of your pan. I recommend starting with one cup and adding more if needed.

Add a few donuts to the oil at a time, and heat for one minute, or just until the bottoms begin to turn golden in color. Flip the donuts and heat the other side for one minute or until they begin to turn golden in color.

Transfer the cooked donuts to a cooling rack lined with paper towels to soak up excess oil.

Mix the glaze together at the end of second rise just before you plan to cook the donuts. In a small bowl stir together the milk and powdered sugar until you have a thin runny mixture with no lumps.

After cooking, allow your donuts to cool for a few minutes and then dip one side into the glaze. Place the freshly glazed donuts glaze side up on a drying rack, and allow the glaze to set for 10 minutes before serving.