If using sheets of graham crackers, place them in a storage bag. Crush them into fine crumbs using a rolling pin. Set aside.
Place the butter and peanut butter into a medium microwave-safe bowl. Microwave for 1 minute and stir until the peanut butter is incorporated.
Add the vanilla extract and stir in until combined.
Place the graham cracker crumbs and powdered sugar into the butter/peanut butter mixture. Stir with a spatula until everything is incorporated.
Place the crumb mixture into the prepared pan and press it firmly and evenly into the bottom.
In a small microwave-safe bowl, add the chocolate chips and vegetable oil. Microwave in 30-second intervals and stir after each interval until the chocolate is completely smooth. My chocolate took 3 intervals of 30 seconds to melt and smooth out.
Pour the chocolate onto the 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.
Store in an airtight container or covered with plastic wrap at room temperature or for a firmer bar in the refrigerator.
Notes
Storage: Store in an airtight container or ziploc-style storage bag. They can be stored at room temperature or for a firmer bar in the refrigerated. They will last from 7 to 14 days.Freezing: Place in a freezer-safe container or freezer bag. Freeze them for 2-3 months. Then, eat straight from the freezer or let them thaw on the counter for 1 to 2 hours or overnight in the fridge.