Preheat oven to 350 degrees F.
Prepare three 8-inch round cake pans by spraying them with baking oil and adding parchment paper to the bottom, and another coating of baking spray.
After you have cleaned and grated the carrots, squeeze until most of the liquid comes out. Set aside two cups of shredded carrots.
In a large bowl using a hand mixer, or in the bowl of a stand mixer, fitted with the wire attachment, beat together eggs, oil, vanilla, and sugar. Fold in the shredded carrots.
Slowly add in the flour, salt, baking powder, and baking soda followed by the kefir.
Using a rubber spatula, manually gently fold in the hazelnuts and the blackberries. Divide batter evenly between prepared cake pans.
Bake 40-45 minutes in the preheated oven, or until a knife/toothpick inserted in the center of a cake comes out clean. Rotate the cakes mid baking and switch racks (cakes from upper rack to lower rack and vice versa).
Cool for 20 minutes in pans, then move cake to a wire rack to cool completely before frosting.