Preheat oven to 350 degrees. In a small bowl, sift together the dry ingredients and set aside. Cream the butter and sugar in the bowl of an electric mixer using the paddle attachment. Add the egg and vanilla and beat until combined. Add the peanut butter and continue beating on low speed. Add the sifted dry ingredients and beat until just blended.
Form dough into 1 1/2 inch balls. Roll balls in turbinado sugar. Place each ball in a cup of a greased mini muffin tin. Bake 10 to 12 minutes until edges are browned and crackled, the centers will not be completely set. Remove the cookies from the oven and using the end of a thick-handled wooden spoon make a small, deep well in the center of each cookie and fill with Nutella. Sprinkle chopped peanuts on top of Nutella. Transfer cookies to a rack to cool completely.
Tip: Don’t worry about smoothing the Nutella at first. After you’ve put Nutella in each cookie go back and spread it. It will have melted a bit and be much easier to spread.