• Preheat the oven to 350 degrees Fahrenheit. Spray a 9in cake pan or springform pan with nonstick spray. Line the bottom of the pan with parchment paper. Set aside.
• Cream together the butter and the sugars in a large bowl.
• Add in the egg and egg yolk and the vanilla and stir in.
• In another bowl mix together your baking soda, salt and flour.
• Add the dry ingredients to the wet ingredients and stir everything together till just combined.
• Add in the white chocolate chips and Oreo pieces and fold them into the batter.
• Press the cookie dough into the prepared cake pan.
• Bake in the preheated oven for 20-25 minutes until the cookie is golden brown.
• Allow the cookie cake to cool for in the pan. Loosen the sides with a knife and transfer carefully to a platter or serving dish.

For the Buttercream Frosting:

• Add the butter and powdered sugar to a large bowl and beat them together until combined.
• Add in the cream, vanilla extract, and salt and beat them into the frosting. (Add more cream, or powdered sugar as needed to get the right consistency)
• Continue beating the frosting for a couple minutes over high speed until it is soft and fluffy.
• Decorate cookie edges with buttercream frosting using a 1M tip.
• Slice and serve.