1. Preheat the oven to 350 degrees.
2. Combine flour, baking soda, and cornstarch in a bowl.
3. In a separate bowl, whisk together the melted butter, brown sugar, egg, and vanilla until smooth.
4. Using a wooden spoon, mix together the wet and dry ingredients, then fold in the Utoffeea crumble. Dough will be soft, but thick.
5. Using a small cookie scoop, fill 2 cookie sheets with 12 mounds each. Refrigerate or freeze for about 10 minutes before baking (this will prevent the cookies from spreading too far during the bake).
5. Bake at 350 degrees for approximately 10 minutes. Once cookies are out of the oven, top each cookie with a small amount of Utoffeea crumble for that WOW factor!
These cookies will stay fresh in a sealed container for 3 days - if they last that long!