Place hazelnuts on a sheet pan and toast at 350°F for 9-10 minutes. While still hot, transfer the hazelnuts into a kitchen towel and rub together vigorously to remove most of the skins. Coarsely chop the hazelnuts and set aside. (Note: The skins come off easier while hot, and the kitchen towel allows you to handle the hot hazelnuts. Don't worry if some skins remain.)

In the bowl of a countertop mixer fitted with the paddle attachment, add the butter, sugar, salt, vanilla, and baking powder. Mix on medium-low speed until mixture is fully combined and smooth.

Add the eggs and mix on low speed until fully absorbed.

Add the flour and chopped hazelnuts and mix on low speed until fully combined.

Transfer dough to a lined baking sheet and shape into a 5"x10" log.

Sprinkle a generous amount of turbinado or sanding sugar across the top of the log. (optional)

Bake at 350°F for 25 minutes.

Remove pan from oven and allow it to cool for 7-8 minutes. Transfer biscotti to a cutting board and use a sharp knife to slice the log crosswise into 3/4" slices. Place each biscotti cut-side down on a lined-baking sheet.

Reduce oven temperature to 325°F and continue baking for another 25-30 minutes, or until the biscotti begin to turn golden brown.