Combine all of the ingredients together is a large bowl, and mix on medium speed until combined and “smooth”.
Let sit while you prepare your cookies.
In a large bowl using a hand-held mixer or stand mixer (paddle attachment optional), beat the butter, brown sugar, and sugar together on medium speed until combined and creamy, about two minutes. Beat in the egg and vanilla. Scrape down the sides and bottom of the bowl as needed.
In a separate bowl, combine flour, cornstarch, baking soda and salt. Then add your dry mixture into the the wet ingredients, and beat on low speed until combined and batter appears thick.
On low speed, mix in the chocolate chips.
Cover dough tightly with aluminum foil or plastic wrap and chill for at least one hour (up to two days). Chilling is mandatory for this recipe as it allows the ingredients to properly distribute. After an hour, remove cookie dough from the refrigerator and allow to sit at room temperature for ten minutes.
Preheat oven to 350°. Line two large baking sheets with parchment paper or silicone baking mats. Note: Once chilled, the dough will be slightly crumbly, but will come together when you work the dough with your hands. Roll balls of dough, about 2 tablespoons of dough each, into balls.
Place the dough balls on to the baking sheets and make a small indent with your thumb or spoon. Pour your butter tart filling into the indented space, and add crush pecan on top.
Bake for 10-12 minutes, until barely golden brown around the edges. Note: The cookies will look extremely soft when you remove them from the oven. Cool for five minutes on the baking sheet (They do their last bit of baking out of the oven). They might be slightly puffer, but the cookies will slightly deflate as you let them cool.
Transfer cookies to a cooling rack to cool completely. Cookies stay fresh covered at room temperature for up to one week.
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