Preheat your oven to 350°F (175°C). Grease three 8-inch round cake pans with butter or oil and line the bottoms with parchment paper.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 tablespoon of baking powder, 1 teaspoon of baking soda, and ½ teaspoon of salt.

In another bowl, beat ½ cup of vegetable oil and 1 cup of granulated sugar together until creamy. Gradually add in ½ cup of sour cream, mixing until smooth.

Gradually add the flour mixture to the wet ingredients, alternating with 1 cup of milk. Mix until just combined, then fold in 3 whipped egg whites and 1 cup of chopped Oreos.

Divide and bake the batter in the prepared pans for about 30-35 minutes, or until a toothpick comes out clean. Let cool in pans for 10 minutes before transferring to a wire rack.

Melt 8 ounces of white chocolate. Combine with 1 cup of heavy cream while warm. Add 8 ounces of cream cheese and mix until smooth, then fold in 1 cup of whipped cream and ½ cup of chopped Oreos.

Beat ½ cup of butter and 8 ounces of cream cheese until creamy. Gradually add in 2 cups of powdered sugar and 1 cup of pulverized Oreos.

Place one cake layer on a cake stand. Spread a layer of white chocolate mousse over it, followed by a layer of frosting. Repeat with remaining layers.

Prepare the ganache by heating ½ cup of heavy cream. Pour it over 6 ounces of semi-sweet chocolate, let sit, then stir until smooth. Drizzle over the assembled cake.

Chill the cake for 30 minutes, then decorate with halved Oreos and cookie crumbs.