First, make the chocolate chip cookie bars. Preheat oven to 325 degrees F. Spray a 9x13-inch baking pan with nonstick cooking spray and set aside.
In a medium bowl, whisk together flour, salt, and baking soda. Set aside.
In the bowl of a stand mixer, mix the melted butter and sugars together until combined. Add the egg, egg yolk, and vanilla extract and mix until smooth. Slowly add the dry ingredients and mix on low, just until combined. Stir in the chocolate chips.
Pour cookie dough into the prepared pan, smoothing the top with the spatula. Sprinkle cookie bars very lightly with sea salt, if desired. Bake cookie bars for 25-30 minutes or until the top of the bars are light golden brown and the edges start to pull away from the pan. Remove bars from oven and cool completely.
When the cookie bars are completely cool, evenly spread the ice cream over the cookie bars. Garnish with chocolate chips.
Cover the ice cream bars and place in the freezer. Freeze until ice cream hardens, at least 2 hours. This dessert can be made in advance.
When ready to serve, remove the pan from the freezer. Run a sharp knife under hot water and cut the bars into squares. The bars will be hard to cut so make sure you get the knife super hot in between each cut. Drizzle the bars with hot fudge sauce, if desired. Serve.
Note-To soften the ice cream, let the ice cream out on a countertop for 30 minutes before using. You want it soft enough to spread over cookie bars but still slightly frozen. The ice cream bars will be hard to eat with a fork if you eat them straight from the freezer. You can let them sit for a bit or you can pick them up and eat them. They are a little messy to eat, but I promise it is worth the mess!