Pack the base down hard — a loose base is the only thing that makes these crumble when you cut them. A bench scraper or sharp knife wiped between cuts gives the cleanest squares.
Instructions
Line a 9x13 pan with parchment, leaving an overhang on two sides.
Stir the graham crumbs, ¾ cup peanut butter, ½ cup melted butter, and the powdered sugar together until it forms a stiff dough.
Press the mixture firmly and evenly into the lined pan. Use the bottom of a measuring cup to pack it flat.
Melt the chocolate chips with the remaining ¼ cup peanut butter and ¼ cup butter, stirring until smooth.
Pour the chocolate layer over the base and spread to the edges.
Chill at least 2 hours, until firm, then lift out by the parchment and cut into 16 bars.