Preheat oven to 350 degrees. Prepare a 9” springform pan or a 9” cake pan with non-stick spray. Note: The springform pan allows for easy removal of the sides, if you use a regular cake pan it will be difficult to remove from the pan.
In a medium sized bowl, whisk together the flour, cornstarch, baking soda and salt. Set aside.
In a large bowl, using a hand mixer or stand mixer, beat together the melted butter, brown sugar and granulated sugar.
Add in the egg, egg yolk and vanilla and mix until just combined.
Slowly add the dry ingredients into the wet ingredients and mix together until well combined.
Fold in the chocolate chips and pecans with a spatula.
Scoop the dough into the prepared pan and spread it to the edges of the pan. Bake for 25-27 minutes, until the edges start to brown and a toothpick comes out clean. Set aside and allow the cookie cake to completely cool (90 minutes recommended) before frosting and adding the caramel.
While the cookie cake is cooling, prepare the frosting.
In a small saucepan, melt together the butter and unsweetened chocolate on medium/low heat. Set aside and allow the chocolate mixture to cool for 10-15 minutes, just until it’s no longer hot.
In a small bowl, using a mixer combine together the cooled chocolate, vanilla, powdered sugar and half of the milk. Add in a little more of the milk only as needed; stop adding when the desired consistency has been reached.
When the cookie cake is ready to be decorated fill a piping bag with the prepared frosting and a tip of your choice; I used 1M for the tip. Decorate the edges of the cake.
Drizzle the caramel all over the top or on slices before serving.