Next, grease donut pan(s) with non-stick cooking spray.

After that, combine both flours, granulated sugar, baking powder, salt, and baking soda in a large bowl. Whisk all the ingredients together.

Then, add the butter to the bowl using a pastry cutter. The mixture should look like grainy sand. 

Afterward, in a separate bowl, whisk the eggs until they are frothy and then add the sour cream and vanilla. Stir everything together to make sure they are smooth and creamy.  

Now, mix the wet and dry ingredients together to create the dough.

Lastly, put the dough into a pastry bag and fill the donut pan(s) with the batter. Each donut should be filled 2/3 full so that they can rise properly. Bake them for about 10 to 15 minutes. Remove the pan(s) from the oven so they can cool off before you glaze the donuts.

First, in a small bowl, sift together the powdered sugar and cocoa powder to remove any lumps.

Next, in a separate small bowl, warm the Nutella in the microwave for 10-15 seconds on high (just enough to make it easier to stir).

Now, combine the powdered sugar, cocoa, Nutella and milk and stir them together. If the glaze is too thick, add additional milk (1 teaspoon at a time). However, if the mixture is too thin, then add extra powdered sugar (1 teaspoon at a time).

Last, dip the top of one donut into the glaze and let the excess drip off. You can place on a cooling rack to set. Continue the process with the remaining donuts.