Preheat oven to 350°F (177°C).

Stir the graham cracker crust ingredients together. Pour into a 9-inch tart pan and pack in very tightly. The tighter it’s packed, the less likely it will fall apart. I recommend using the bottom of a flat-bottomed measuring cup to pack it into the bottom and around the sides. Bake for 13–15 minutes or until very lightly browned around the edges. Remove from the oven and allow to cool for 15 minutes before adding the filling. It’s best if the crust is still slightly warm so the filling can properly adhere.

Using a hand mixer or a stand mixer fitted with paddle attachment, beat the softened butter on medium-high speed until completely smooth and creamy, about 2 minutes. Add the confectioners’ sugar, vanilla extract, and salt, and beat until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl as needed. Add the peanut butter and beat until smooth and combined.

Spread filling evenly into tart crust. Set aside as you prepare the topping.

Using a double boiler or microwave, melt the chocolate and peanut butter together until smooth. If using the microwave, stop and stir every 15 seconds until melted. Pour and spread over filling. (For the pictured tart, I saved 1–2 Tablespoons of the topping and drizzled it on top after the topping set.)

Chill in the refrigerator, uncovered, for 4–6 hours (or up to 2 days) before slicing. If chilling for longer than 6 hours, cover it. This crust is crumbly no matter what, but chilling for 6+ hours helps the tart slice a little neater.

Cover leftovers tightly and refrigerate for up to 1 week.