1. In a large bowl, cream together the softened butter, egg, and egg yolk until smooth and glossy.
2. Gradually incorporate the cookie mix into the wet ingredients. Use a spatula to mix until just combined. Avoid overmixing.
3. Press the cookie dough evenly into the prepared springform pan and refrigerate for 36 hours. YES, 36 hours 🙂. 
4. Preheat your oven to 350°F (177°C). Grease a 9-inch springform pan with non-stick cooking spray.
5. Bake the cookie cake for 28-33 minutes, or until the edges are golden brown. The center may still be slightly soft, which is characteristic of a good cookie cake.
6. Sprinkle with sea salt, freshly out of the oven, while the cookie cake is still soft.
7. Let the cookie cake cool completely in the pan before removing the sides of the springform pan.
   
   

Tips:

• If you prefer a chewier cookie cake, bake for a shorter time. Conversely, for a crispier cake, bake for a few extra minutes.