Line an 8×8 or 9×9 inch baking pan with aluminum foil or parchment paper. Spray with cooking spray.
For the peanut butter layer: In a medium bowl, mix together the butter, gluten-free graham cracker crumbs, powdered sugar and salt. Stir in the peanut butter until evenly combined.
Press the peanut butter mixture evenly into the prepared baking pan.
For the chocolate topping: Add the peanut butter and chocolate to a small microwave-safe bowl. Microwave for 1 minute until the chocolate is melted and the mixture is smooth, stirring every 15 seconds.
Spread the chocolate topping over the peanut butter layer.
Cover and refrigerate for at least 2 hours or up to 5 days. Let sit at room temperature for 10 minutes before slicing and serving.