Preheat oven to 350F and grease and flour three 6” cake rounds.
Whisk together flour, sugar, baking soda, salt, and baking powder in a bowl.
Add butter, and beat well with a hand mixer or in a stand mixer with the whisk attachment, until the mixture resembles fine crumbs.
In a separate bowl, whisk together egg, sour cream, vanilla, and oil until combined.
Pour wet ingredients into the flour and butter mixture, and beat on medium for 3-4 minutes. The mixture will be dry at this point.
Add in water and mix until just combined. Fold in the crushed Oreos. Do not overmix.
Spread batter evenly into prepared pans. Smooth the tops with a spatula.
Bake for approx. 20-25 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on a wire rack to cool for 20 mins then turn out onto wire rack to cool completely before removing from pan.