Preheat the oven to 350℉ and grease and flour dust 2X8-inch pans, and set them aside.
Spread the hazelnuts on a baking sheet and roast them in a 350F oven for 10-15 minutes. Keep an eye on them, as nuts burn very easily.
½ cup Hazelnuts
Using the food processor, grind the hazelnuts. Sift them with other dry ingredients and set them aside.
1¾ cups All-purpose flour, 2 teaspoon Baking powder, ½ teaspoon Salt, 1 teaspoon Cinnamon
Using the whisk attachment, whisk the eggs for 5-7 minutes. This will aerate the eggs and contribute to the spongy and fluffy texture.
4 Eggs
Add the orange zest to the sugar and rub it into the sugar with your fingertips. This will release the orange aroma and oil. While the eggs are whisking, gradually add the sugar and keep beating. The mixture should become creamy, thick, and pale in colour.
1 cup Sugar, 1 tablespoon Orange zest
Mix the melted butter, oil, sour cream, milk, vanilla extract, and orange juice in a separate bowl. Add the dry ingredients to the egg mixture, alternating with the wet ingredients. Do this in three passes, starting and finishing with the dry ingredients. Do not overmix the batter, and stop mixing when there is no trace of dry ingredients.
½ cup Butter, 1 tablespoon Oil, 2 tablespoon Sour cream, ¼ cup Milk, 2-3 tablespoon Orange juice, 1 tablespoon Vanilla extract
Pour the batter into the prepared pans and bake them for 25-30 minutes or until an insert comes out clean. Let the cakes cool down in the pan, then flip them onto a cooling rack. Let them cool down completely before frosting.