Place the crackers in a Ziplock bag and use a rolling pin to finely crush the graham crackers into crumbs. They sell prepackaged graham cracker crumbs at the store, if you want to save a little work.
Place crumbs into a medium microwave-safe bowl. Add in the butter and microwave for 30 second intervals. Stir after each interval. Mine took 1 minute for the butter to melt completely.
Place the peanut butter and powdered sugar into crumb mixture. Mix with a spatula until everything is incorporated.
Place the crumb mixture into the prepared pan and press it into the bottom of the pan. Make sure it's firmly packed.
In a small microwave-safe bowl, add in the chocolate chips and shortening. Microwave for 30 second intervals until the chocolate is completely smooth. Make sure to stir after each time in the microwave. My mixture took 3 intervals of 30 seconds to completely melt and smooth out.
Pour the chocolate onto the peanut butter crumb mixture and smooth out. Make sure it is spread to all the edges.
Refrigerate for 1 - 2 hours or until the chocolate top is firm. Cut into squares and serve.