Preheat the oven to 350℉ and grease a 12-cavity donut pan with oil spray. Set it aside.
Sift the flour, salt, baking powder and soda.
1¾ cups All-purpose flour, 2 teaspoon Baking powder, ½ teaspoon Baking soda, ¼ teaspoon Salt
Add in the ground hazelnut and mix well. Set them aside.
1 cup Hazlenut
Use the whisk attachment to beat the sugar, oil, and butter. The mixture will become smooth and creamy.
1 cup Brown sugar, ½ cup Oil, 1 tablespoon Butter
Add the eggs one at a time and beat them thoroughly after each one.
3 Eggs
Add vanilla extract and mix well.
1 tablespoon Vanilla extract
Mix in the sour cream.
½ cup Sour cream
Gently fold in the dry ingredients and mix slowly. Do not overmix.
Use a small spoon or a piping bag to transfer the batter into the donut pan's cavities. Do not over-fill the cavities.
Bake them for 10-12 minutes. They are ready when their edges look set, and an insert comes out clean. Let them cool in the pan for ten minutes, and then transfer them to the cooling rack to cool completely.
How To Make The Glaze
Wisk all the ingredients until the mixture is smooth and homogenous.
1 cup powdered sugar, 2 tablespoon Nutella, ½ teaspoon Vanilla extract, 3-4 tablespoon Milk
If the mixture is too runny, add one tablespoon of powdered sugar, and if it is too stiff, add one tablespoon of milk. The mixture should have the consistency of warm honey.
Dip the top of the donuts, the side touching the pan, into the glaze, and let them set on the rack. Top them with crushed hazelnut and Let them sit on the rack until the glaze sets and hardens.