Directions

1. Preheat oven to 350F and line two cookie sheets with parchment paper. One cookie sheet will be for the hazelnuts, and one will be for the cookies.
2. Place hazelnuts on a cookie sheet and roast for 10-15 minutes or until the skins begin to brown. Allow to cool for 5-10 minutes, then transfer to a clean kitchen towel and rub together to get the skins off- the skins are bitter!
3. Adjust oven to 375F.
4. Add hazelnuts to a food processor or high-speed blender and blend until a smooth butter forms (about 5 minutes), then add all other ingredients (hazelnut oil, sugar, cocoa powder, vanilla extract, and sea salt) and blend until smooth. Transfer to an airtight container for up to two weeks, or in the refrigerator for up to two months. Alternatively, you can make this ahead of time and use it when you are ready to make the cookies.
5. Make the cookies: in a mixing bowl, beat the butter with an electric mixer on medium to high speed until smooth and creamy (about 1 minute). Add in half the flour (3/4 cup), sugar, egg yolks, hazelnut oil, vanilla extract, and salt and beat until combined. Add remaining flour.
6. Using a 1-inch cookie scoop, scoop dough to form balls. Roll in egg whites, then into the chopped walnuts and transfer to lined cookie sheet. Press centers with your thumb and bake at 375F for 10-12 minutes, or until edges are lightly browned. Allow cookies to cool before filling with homemade Nutella. Makes about 18-20 cookies.