In a bowl add sugar, flour, cocoa powder, baking powder, baking soda, salt together. Mix until combined.
Then add egg, buttermilk, oil, vanilla extract, and water to the dry ingredients and mix well.
Line a baking 9x5 baking pan with parchment paper and pour batter into pan. Bake for 20-22 minutes until cake is done. Remove from oven and cool completely.
Crush oreo cookies into small pieces. In a large bowl combine with thawed ice cream.
Add oreo ice cream mix on top of the cake. Fold over parchment paper flap. Freeze for 3-4 hours until set. Enjoy.