Prep the pan. Line an 8x8-inch baking pan with parchment so it overhangs on two sides. This makes lifting the bars out easy and keeps edges neat.

Warm the base mixture. In a medium saucepan over low heat, melt the butter. Stir in 1 cup peanut butter and salt until smooth. Take off the heat.

Sweeten and thicken. Add vanilla. Stir in powdered sugar until no streaks remain. Fold in graham cracker crumbs until evenly combined and it looks like soft cookie dough.

Press the base. Transfer the mixture to the lined pan. Press firmly into an even layer using the bottom of a measuring cup. Pack the corners so the top layer adheres well.

Make the topping. In a clean saucepan or microwave-safe bowl, gently melt chocolate chips and 2 tablespoons peanut butter, stirring until glossy. Avoid overheating to keep it smooth.

Top and smooth. Pour the warm chocolate mixture over the base. Tilt and use an offset spatula to spread it into a thin, even layer. Tap the pan lightly on the counter to pop air bubbles.

Chill to set. Refrigerate for 1–2 hours, until the topping is firm to the touch. For quicker slicing later, don’t freeze solid at this stage; you want it cold but not rock hard.

Slice cleanly. Lift the slab out by the parchment. Warm a sharp knife under hot water, dry it, and cut into 16–25 bars. Wipe the knife between cuts for tidy edges. Sprinkle with flaky salt just before serving if you like.