In a large bowl, whisk together flour, baking soda, cornstarch, cinnamon and salt. Set aside.
In a separate bowl, whisk melted butter with brown sugar, until smooth and not lumpy.
Whisk the egg into the butter and sugar mixture, then add the vanilla extract.
Pour the butter mixture into the flour mixture and mix until fully combined. Dough will be thick.
Cover dough with plastic wrap and refrigerate 3 hours or up to 2 days.
Remove from fridge after chilling and allow to soften a bit before handling, about 10 minutes.
Preheat oven to 325°F and line baking sheets with parchment paper
Pour white sugar into a shallow bowl
Roll dough into balls using about 2 Tbsp of dough, then roll in sugar before placing 3 inches apart on parchment lined baking sheets
Bake 8 minutes, then remove from oven and press down gently on each ball with the back of a spoon
Return to oven and bake an additional 2-3 minutes.
Cool on pan for 10 minutes before transferring to cooling racks to finish cooling
Store in an airtight container at room temperature for up to one week.
