Preheat your oven to 350ºF (175ºC) and line three 20 cm baking pans with parchment paper.

Crush 8 Oreo cookies into fine crumbs, separating the filling for later use. Whisk together Oreo crumbs, flour, baking powder, baking soda, and salt.

Cream the reserved Oreo filling with softened butter, vegetable oil, and sugar on high for about 2 minutes until light and fluffy.

Add eggs one at a time on low speed, mixing just until combined for a fluffy texture.

Alternate adding the dry mixture with buttermilk, starting and ending with the dry ingredients, mixing until just combined.

Divide the batter among the three pans, smooth tops, and bake for 20-22 minutes. Cool cakes in the pans on a wire rack.

Beat softened butter and reserved Oreo filling for frosting until fluffy, then gradually add cream cheese and sifted powdered sugar until smooth.

Assemble the cake by spreading frosting between layers, applying a thin crumb coat, and chilling for 20 minutes.

Spread remaining frosting over the cake and garnish with crushed Oreo cookies.