Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper and set aside.
In a large mixing bowl, cream together the peanut butter, butter, and vanilla extract until smooth. Gradually add the brown sugar and beat until well combined.
Add the eggs, one at a time, beating well after each addition.
Add the flour in two batches, mixing just until combined. Fold in the chopped peanuts.
Spread the batter evenly into the prepared baking pan.
Bake for 30 minutes, or until the center is set and a toothpick inserted near the center comes out with a few moist crumbs.
Cool in the pan for 15 to 20 minutes. Using the parchment paper, lift the blondies from the pan and place on a wire rack to cool completely.
Cut into 2-inch bars and dust with powdered sugar before serving.