Preheat the oven to 350° F. Spray 3, 6” pans or 2, 8” pans with baking spray or line with parchment paper and set aside.
In a medium size mixing bowl combine the flour, baking soda, and salt, and whisk lightly to combine.
In another bowl or the bowl of a stand mixer fitted with the paddle attachment, add the oil, brown sugar, and cookie butter. Mix or beat on low- medium until a smooth batter forms. Add in the vanilla and one egg at a time, mixing in between.
Next add ⅓ rd of the dry mixture and alternate adding buttermilk- starting and ending with the flour- usually ⅓ of the flour at a time, and ½ of the buttermilk at a time. Mix on medium speed or with a spatula until a thick smooth mixture forms.
Pour even amounts into your baking pans. Bake 30-35 minutes for 6” pans or 25-28 minutes for 8” pans.
The cakes are ready when the edges start to pill away from the sides and when a toothpick inserted into the middle comes out clean.
While the cakes are cooling make the buttercream. You will need to clean your mixer if you used it for the cake.
Add the butter, cookie butter and confectioners sugar to the bowl of a stand mixer fitted with the paddle attachment. Start the mixer on low speed so that the sugar doesn’t blow up in your face. Gradually increase the speed to medium as more and more sugar gets mixed in. Scrape down the sides as necessary. Add in the amount of half n half needed depending on which type of cookie butter you're using, and depending on how thick or creamy you like your buttercream. If it's too loose add more confectioners sugar. If it’s too thick, add a little more half n half.