Preheat oven to 350. Cream butter, peanut butter, sugars, salt, soda, egg, and vanilla. Mix until well blended. Stir in flour until dough is crumbly. Drizzle Nutella on top of the dough then swirl it through the dough with a butter knife. Chill dough 15 minutes in the refrigerator. Roll into balls by hand. Place on parchment lined cookie sheet. Using a fork, press down the balls to flatten slightly. Bake until edges are very lightly browned (about 7 to 10 minutes). Allow to rest 2 minutes on cookie sheet before transferring cookies to a cooling rack.