Preheat your oven to 350°F (175°C). This ensures that your cake bakes evenly.
Grease your 9-inch round cake pan with a little butter or line it with parchment paper for easy removal.
In a large mixing bowl, combine the melted unsalted butter, granulated sugar, and brown sugar. Use a whisk or electric mixer to blend them until smooth. Add the egg and vanilla extract, mixing until fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry mixture to the wet ingredients, stirring gently until just combined. Be careful not to overmix!
Gently fold in the chocolate chips, ensuring they are evenly distributed throughout the batter.
Pour the batter into the prepared baking pan, smoothing the top with a spatula. Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
While the cake is cooling, make the frosting. In a medium bowl, beat together the softened butter, powdered sugar, cocoa powder, salt, vanilla extract, and 1 tablespoon of heavy whipping cream. Mix until creamy and smooth, adding more cream as needed to achieve your desired consistency.
Once the cake is completely cool, spread the frosting on top using a spatula. Feel free to decorate with additional chocolate chips or sprinkles for an extra touch!
Slice your cookie cake into wedges, serve, and enjoy this delightful treat!