Preparation Steps

• Preheat oven to 350°F (176°C) and prepare three 8-inch cake pans by greasing the sides and lining the bottoms with parchment paper.
• In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
• In a large bowl, cream together butter, vegetable oil, and sugar until light and fluffy, about 3-4 minutes.
• Add eggs one at a time, beating well after each addition. Scrape down the sides as needed.
• Add half the flour mixture to the wet ingredients and mix until combined.
• Pour in buttermilk and vanilla extract and mix until incorporated.
• Add remaining flour mixture and mix until smooth. Do not overmix.
• Fold chopped Oreos into the batter gently.
• Divide batter evenly among pans and bake for 18-23 minutes or until a toothpick inserted comes out with a few crumbs.
• Allow cakes to cool for 2-3 minutes in pans, then transfer to wire racks to cool completely.
• To make buttercream, beat butter until smooth.
• Gradually add half the powdered sugar, beating until smooth.
• Add vanilla extract, 4-5 tablespoons water or cream, and salt; mix until smooth.
• Add remaining powdered sugar gradually and mix until smooth. Adjust water or cream as needed for desired consistency.
• Level cakes by trimming domes off the tops with a serrated knife if necessary.
• Place first cake layer on a serving plate or cake board.
• Spread about 1 cup frosting over the first layer, then sprinkle with 0.5 cup chopped Oreos, pressing them gently into the frosting.
• Repeat with second cake layer, frosting, and Oreos.
• Top cake with last layer and frost the entire outside smoothly.
• Press chopped Oreos onto the frosted sides of the cake while the buttercream is still fresh.
• Pipe buttercream swirls around the top edge and garnish with Oreo halves between swirls.