Step 1

Line a 9×9-inch baking pan with parchment paper, leaving enough overhang on the sides for lifting the bars out of the pan once set.

Step 2

In a large bowl, whisk melted butter and peanut butter until smooth and creamy. Add powdered sugar and whisk until smooth. Add graham cracker or vanilla wafer crumbs and mix until combined. Spread evenly onto prepared baking sheet. Chill mixture while you make the chocolate topping.

Step 3

In a small heat-proof bowl, place chocolate and peanut butter. Melt in the microwave in 20 second intervals, stirring between each, until melted. Alternatively, set over a saucepan of simmering water while stirring occasionally. Spread evenly over peanut butter layer. Refrigerate for at least 2 hours until firm, then lift the bars out of the pan using the parchment paper and cut into squares.

Step 4

Store bars in an airtight container in the fridge for up to a week.