Combine butter, peanut butter, sugars, egg, and vanilla. Blend together very well.
Add flour, baking soda and salt with mixer. If using Nutella, just drizzle it on top of the dough (use more or less to suit your taste) then swirl it through the dough with a butter knife. Chill dough 15 minutes in the refrigerator. Roll into balls by hand.
Place on greased cookie sheet. Using a fork, press down the balls and create a criss-cross pattern. Bake in a preheated 350 degrees F (175 degrees C) oven until edges are very lightly browned (about 7 to 10 minutes). Don't overbake.