Preheat oven to 375 degrees F. Line a baking sheet with parchment paper or a silicone sheet and set aside.
In a large mixing bowl, mix together the flour, sugar, baking powder, baking soda, and cocoa powder.
In a small mixing bowl, whisk together the egg, milk, oil and vegan sour cream.
Add the wet ingredients to the dry and mix with an electric mixer at medium speed until well combined.
Add the chopped walnuts and stir until they are well incorporated.
Cover bowl with a cloth or plastic wrap and chill for one hour.
Place oil in a Dutch oven and heat to 375 degrees F.
On a lightly floured surface, using a floured rolling pin, roll out the dough to 1/2 inch thickness. Cut the dough into 10 even pieces. Shape each into uniform bar shapes about 2-1/2 by 3-1/2 inches. Score each down the center.
Fry donuts in batches of two or three in the oil for about 10-20 seconds. Watch them closely as they burn very quickly and easily.
Once fried, remove from heat and place on a paper towel lined baking rack. Pat to remove excess oil.
Once all the donuts are fried, transfer them to the baking sheet and bake for 8-15 minutes.
While the donuts are baking make the glaze by whisking together the powdered sugar and water until smooth. Add additional powdered sugar or water if needed.
Remove donuts form the oven and transfer to a baking rack. While they are still hot brush them all liberally with glaze. Let them cool and the glaze to harden on the rack.