In a medium-sized bowl, stir together the flour, cornstarch, baking soda, and salt, set aside.
In a large bowl, whisk together the butter and brown sugar until smooth.
Add the egg, vanilla, and butter extract.
Whisk to combine until it is smooth.
Add the flour mixture to the bowl.
Stir it in until combined with no dry patches. This may take a few minutes.
Add the pecans and fold them in.
Line a sheet tray with parchment paper. Using a 1.5 tablespoon cookie scoop, or heaping tablespoon-sized dollops, portion the cookie dough and place them, not touching, but close together on the parchment paper. Cover and place in the refrigerator for two hours, up to overnight.
Preheat the oven to 350°F. Line sheet trays with parchment paper. Take the cookie dough balls and roll them between your hands to form a smooth ball, they will be hard at first but will soften up. Roll them in the decorators sugar and place them on the sheet trays 2 inches apart.
Gently press the pecan halves on to the tops of the cookies, if using.
Bake for 9-10 minutes until the cookies are puffed, the tops are not shiny, and they are slightly browned.
Let them cool on the sheet tray for 10 minutes, then transfer the cookies to a wire rack to cool completely.