• Preheat oven to 350°F. Prepare pans baker’s floured cooking spray, or grease and line with parchment rounds.
• Mix together all dry ingredients (flour, baking powder, sugar, and salt) in a stand mixer with a paddle until fully combined.
• Mix chunks of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mix becomes crumbly.
• Pour in eggs and mix on low until just incorporated.  Mix in the buttermilk. Add in vanilla and oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on medium speed for about 30 seconds. Stir in crushed oreos and rainbow jimmies – the I stirred as little as possible after this point, to keep the Oreo crumbs from turning my cake layers brown!
• Divide batter evenly between the prepared cake pans (I find a kitchen scale helpful for this part). This guarantees your layers will bake to be the same height.
• Bake for 35-37 minutes (or until a toothpick comes out clean). Allow cake layers to cool for 10-15 minutes on a wire cooling rack before removing from pans. Cool completely before frosting. Set in the fridge or freezer to accelerate the cooling process if desired.
• Once the layers have fully cooled, the caramelized bits can be trimmed from the sides / top of the cake using a serrated knife if desired. Be sure the layers are completely cooled or chilled before trimming. If you try to trim the layers while they’re still warm, they will crumble and break. This is a great time to make your frosting!

Frosting

• Beat together softened cream cheese and butter; slowly add in powdered sugar alternating with milk until frosting reaches desired consistency. Add vanilla and salt if needed and beat until well combined.
• You’ll see in the video my crumb-coat layers was much darker brown than the outer frosting layer – I over-stirred some frosting and turned the color too brown, so I had to make more for the outer layer. Stir as little as possible to keep your frosting light in color!
• Once your cakes are cool, level them (if needed). This can be done with a cake leveler or a large serrated knife and a ruler. Place a smear of frosting on your cake circle (to keep the cake from sliding while you decorate it) and center your first cake layer in the center of the circle. Spread the layer with frosting. Repeat the process with your remaining cake layers.
• Now you're ready to crumb-coat . If you're unfamiliar with crumb-coating, it's just what it sounds like – spreading a thin layer of frosting over the entire outside of the cake to keep crumbs out of your final layer. I usually do this with my large offset spatula.
• Once your crumb coat has set (this takes about 5-10 minutes in the fridge), add your final layer of frosting and smooth. I like to use an offset spatula and bench scraper for this part. As I worked through this part I had to pull out a few larger Oreo chunks that were getting in the way of smoothing my frosting. Fill in the holes with a bit of extra frosting and keep smoothing.
• Once your sides are smooth, set the cake in the fridge or freezer for 10-15 minutes to set the frosting and chill the cake so your ganache drip will set.

Chocolate ganache drip:

• Meanwhile, make your ganache. Place chocolate chips in a heat-proof bowl. Add whipping cream and microwave on half power in 30-second intervals, stirring in between until smooth.
• When your ganache has cooled– it should feel only slightly warm and still be fairly liquid – transfer it to a squeeze bottle or piping bag. A spoon will work if you don’t have either of those, I've  just found spoons to be a little bit more difficult to work with.
• Slowly drizzle ganache around the upper edge of your cake, pausing every inch or so to let more ganache fall in a drip down the side of the cake. Return cake to the fridge or freezer to set the drips.
• Transfer remaining frosting to a piping bag fitted with a star tip, and pipe several large frosting swirls to the top rim of the cake – I used my largest most-open star for this, so the Oreo chunks wouldn’t clog the piping tip.
• Space Oreo cookies in between the frosting swirls, add some crushed Oreos and sprinkles to the tip and base rim of the cake – and you’re done! Enjoy!