Preheat the oven to 350*. Line a 9x13 baking dish with parchment paper. Lightly spray the lined baking dish with baking spray (Baker’s Joy or a generic version). Set it aside.
Add the brownie mix, oil, eggs and water to a medium size mixing bowl. Stir just until combined.
Evenly spread the brownie batter in the prepared baking dish. Bake for 20 minutes. Allow the brownies to completely cool.
Peanut Butter Layer
Using either a stand mixer, or a large mixing bowl and a handheld mixer on medium-high speed, beat the butter for 1 minute, or until smooth.
Add the peanut butter and vanilla, continue mixing on medium-high until the mixture is completely combined and smooth.
Lower the mixer speed to medium-low. Add the powdered sugar 1 cup at a time, mixing well after each cup until well incorporated and smooth.
Once the brownie layer is completely cooled, evenly spread the peanut butter mixture over the brownie layer.
Add the chocolate chips and the heavy cream to a microwave safe bowl. Heat in the microwave for 45 seconds. Stir and continue heating in 15 second intervals until the ganache is completely smooth.
Using either a silicone spatula, or an offset spatula, evenly spread the ganache over the peanut butter layer.
Cover the brownies and chill in the refrigerator for 15 - 20 minutes. Remove the brownies from the refrigerator. Slice 15 slices - 2 ½ in x 3 in, return the covered brownies to the refrigerator to chill for an additional 1 hour 45 minutes.
Remove the brownies from the baking dish by the parchment paper. You may need to carefully re-slice the brownies before serving.
To Store: Store any leftovers in an airtight container for up to 7 days.
To Freeze: You can freeze the buckeye brownies for up to 1 month in a freezer-safe container. Allow the brownies to thaw overnight in the refrigerator before serving.
For easier clean-up line your baking dish with parchment paper before baking. This will allow you to easily lift them out of the pan and slice for serving.
You can let the brownies chill for the full 2 hours before slicing, but the chocolate may crack and not be as pretty as pre-slicing after chilling for the 15 - 20 minutes.
When spreading and smoothing the peanut butter mixture over the brownie layer, you can place a piece of wax paper on top to help smooth the mixture.