Blend flour, baking soda, baking powder, salt, and cocoa - set aside
Beat butter until creamy
Beat in sugar until light and fluffy
Add eggs one at a time
Mix in vanilla
Add ⅓ of the flour mixture and beat in quickly
Add ½ the buttermilk and beat until blended
Repeat ending with the last of the flour mixture
Spoon batter evenly into pans
Bake for 25 to 30 minutes
Filling
Crumble the cookies in chunks, not too big - set aside
Mix the confectioner's and the butter until the mixture is blended and crumbly
Add vanilla - beat well
Add about 2 tablespoons of the cream and beat
Beat in the cream, 2 tablespoons at a time until the mixture is creamy (you may need a bit more cream than ¼ cup)
Stir in the cookies, reserving ½ cup of cookies for the top of the cake
Assembly
When cakes are done remove from oven and let stand for 10 minutes
Remove from pans and cool completely
Slice each cooled cake in half horizontally to make 4 layers total
Place one layer on a cake plate and cover with ⅓ of the filling
Press the next layer gently over the filling
Add ⅓ of the filling
Press the next layer gently over the filling
Add the last ⅓ of the filling and top with the last cake layer
Push 4 straws into the cake around the center to stabilize it and freeze for 30 minutes
Remove from freezer and smooth a thin layer of chocolate frosting over the cake
Freeze for 30 minutes
Remove from freezer and finish frosting the cake
Sprinkle reserved crumbs on top and refrigerate
Let stand 30 minutes at room temperature before serving
Remove straws before serving
Notes
Storage:This chocolate layer cake is safe at room temperature, so you can keep it (and any leftovers) on your counter for about three days. Cover the cake in a cloche or cake carrier if you have one, and keep it out of direct sunlight.It will be fine for 3 or 4 days.You can freeze for up to 3 months.Tips:
I like to use cocoa powder to dust my cake pans so the chocolate cake layers don't have any white residue on the outside.
A simple spray-type vegetable oil works fine to grease the pans, as long as it's not a flavored oil, like olive oil. You can also use butter!
Pulse the Oreo cookies in a food processor for easy prep. Just don't obliterate them into fine crumbs. You want nice chunks for texture.
You can also place the cookies in a freezer bag and whack them with a rolling pin—I recommend this way if you need to release some angst!
It's always a good idea to make sure you can swap ingredients before doing so—some recipes are more finicky than others. In this cake, if you need to replace the buttermilk with something, try one of these buttermilk substitution ideas.
Alternating the dry ingredients with the buttermilk helps combine everything together evenly. By dumping everything in at once, your cake might end up a little greasy and dense.
Don't let the cake batter sit for too long after it's mixed up. It needs to go in the oven pretty quickly!
For best results, let the layers of chocolate cake cool fully before attempting to cut or stack 'em.
If you're nervous about cutting the layers of cake in half, use a ruler and a knife to make small notches all around the edges. Then, as you cut, you can follow the notches as a guide.
Just a hint -- If you have trouble with your cake tops being domed try making a hollow in the center of the cake batter once it is in the pan It doesn't have to be real deep but the sides will rise a little differently than the center and your cake will be flat on top.