In a saucepan melt the butter and oil until hot. Take the saucepan off the heat and add in the chocolate and stir until smooth. Set aside to cool down.
In a stand mixer whip up the eggs, sugars and vanilla until light and fluffy. Slowly add in the warm butter and chocolate mixture and mix on medium until just combined.
Sift the dry ingredients directly into the batter and fold until just combined.
Line an 8x8in baking pan with parchment paper and pour half the brownie batter into the pan. Alternate by adding the Reeses and Oreos on top of the brownie batter. Add in the remaining brownie batter and then top with a few whole pieces of Reeses and Oreos and then a mixture of chopped up pieces.
Bake for 25-35 minutes. Insert a toothpick into the center of the brownie, the brownie is done when there are still some crumbs left.
Allow the brownies to fully cool before cutting. Enjoy!