Line a 9 x 9 inch baking pan with parchment paper; set aside.
In a bowl, use an electric mixer to combine the peanut butter and melted butter. Add in the powdered sugar and mix until just combined. Press the dough into the prepared pan using a rubber spatula or damp hands. Refrigerate for 20 minutes.
For the chocolate topping, melt the chocolate chips and 1 tablespoon of butter in a microwave safe bowl at 50% power, stopping to stir every 30 seconds, until just melted. Spread over cooled bars. Refrigerate until hardened and cut into small squares.
Notes
Be sure to line your pan with parchment so you can easily lift the bars out of the pan and cut them into squares.
If your peanut butter is cold, bring to room temperature before mixing. You can also microwave for a couple of minutes before using.
Microwaving the chocolate is the easiest way to melt it. To do so, just heat it at 50% power, stopping to stir it every 30 seconds until melted.
If you chocolate gets stiff and difficult to spread, just stir in a bit of coconut oil to loosen it up.
Be sure to chill the bars before cutting. Store leftover bars in an airtight container in the refrigerator for up to two weeks. You can also freeze for up to a month.