Line an 8x8 inch (20x20 centimeter) baking dish with parchment.
In a small saucepan, place the butter, peanut butter, brown sugar, and salt over medium low heat.
Cook, whisking often, until the butter is melted and the mixture is smooth.
Remove from heat and whisk in the vanilla extract.
In a large bowl, combine the powdered sugar and crushed graham crackers.
Fold in the melted butter and peanut butter mixture until well combined and no streaks of the sugar remain.
Transfer the mixture into an even layer in the prepared baking dish.
Place the semi-sweet chocolate and peanut butter in a large bowl.
Microwave in 20 second increments, whisking in between, until fully melted and smooth.
Pour the melted chocolate over the peanut butter mixture and use a spatula to carefully smooth over the top without pressing down into the peanut butter. If using, top with sprinkles.
Place the dish in the refrigerator and allow to chill until set, at least 2 hours.
Remove from the refrigerator for about 15 minutes before using a sharp knife to cut into squares.