Preheat the oven to 350 F/180 C.
Butter the bottom and sides of a 9-inch cake pan or springform pan. If using a cake pan, cut two long strips of parchment paper to lay on the bottom and up the sides of the pan (see photo in post for visual). Then line the bottom of the pan with a round of parchment. If using a springform pan, you only need to line the bottom of the pan.
In a stand mixing bowl or with a hand mixer, cream the butter, sugar, and brown sugar together until fluffy.
¾ cup unsalted butter, 1 cup light brown sugar, ¼ cup granulated sugar
Mix in the egg, egg yolk, and vanilla.
2 large eggs, 1 large egg yolk, 2 teaspoon vanilla extract
Fold in the flour, baking soda, salt, and chopped oreos.
2 ⅓ cups all-purpose flour, ¾ teaspoon baking soda, ½ teaspoon salt, 2 cups chopped oreos
Evenly spread the dough into the prepared pan.
Bake for 22-25 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Let the pan cool on a wire cooling rack completely before removing.
Tip: if using a cake pan, have someone help you grab all of the strips of parchment up to remove the cookie from the pan. Then pull the parchment off and place the cookie on a serving plate.
Mix the butter in a stand mixing bowl or with an electric hand mixer until smooth.
6 tablespoon unsalted butter
Gradually mix in the powdered sugar and salt until combined.
¾ cup powdered sugar, Pinch salt
Mix in the vanilla and heavy cream, then mix on medium speed until light and fluffy.
½ teaspoon vanilla extract, 2 teaspoon heavy cream
Fill a pastry bag and use a star tip to decorate the top of the cake.