Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream the butter and sugar on med-high until pale and fluffy (about 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition. Gently fold in chopped Oreos.
Pour batter into prepared pans and bake for about 30 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack.
Golden Oreo Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a pot with 1-2" of simmering water and whisk constantly until the mixture is hot and no longer grainy to the touch or reads 160F on a candy thermometer (approx. 5 mins)
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.**
While buttercream is whipping, place oreo centers into a microwave-safe bowl. Heat in 10 second increments until you can stir them into a paste (make sure it's not warm). Add this paste and the clear vanilla extract to the buttercream and whip until smooth.
Remove about 1 cup of buttercream for dollops on top (more if you want to use this as filling as well).
Add the Golden Oreo cookie crumbs to the remaining buttercream and whip until smooth.***
Place chopped chocolate and cream in a microwave-safe bowl. Heat in 5-10 second increments, stirring in between, until smooth and combined. Add a tiny bit of violet color gel and few drops of bright white color gel to lighten if desired (I did - See this post for more details). Set aside to thicken and cool completely.
Place one layer of cake on a cake stand or serving plate. Top with about 2/3 cup buttercream and sprinkle with chopped Golden Oreos if desired. Repeat with the remaining layers. Do a thin crumb coat all over the cake and chill for 20mins.
Frost and smooth the outside of the cake with the remaining buttercream. Chill for 30mins until firm.
Using a small spoon, place dollops of ganache around the top edges of the cooled cake, allowing some to drip down. Fill in the top of the cake with more ganache and spread evenly with an offset spatula. Allow to set for a few minutes.
Pipe rosette dollops of the white buttercream on top, slightly separated, using a 1M piping tip. Place a mini Golden Oreo in the center of each dollop if desired.
Pipe smaller dollops of the cookie frosting in between the red ones using a 4B tip. Fill in the top and decorate the bottom with crushed Golden Oreos if desired.
Be sure to check my Swiss Meringue Buttercream post for tips and troubleshooting.* Ensure there is no trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease-free or your meringue won't stiffen.** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.*** Make sure this is a very fine powder. I placed the cookies into a large Ziploc bag and used a mallet to crush them I then strained them through a very fine mesh strainer.