Add 1 cup of the divided peanut butter, melted butter, and vanilla extract to the food processor and blend together until a smooth, thick dough forms, about 2-3 minutes.
Line an 8×8 inch baking pan with parchment paper, then scoop in the peanut butter dough. Press the dough down into an even layer, cover with plastic wrap, and place it in the refrigerator to chill.