
Melt butter in large, microwave-safe bowl and allow to cool completely.
Stir in brown sugar and maple syrup until completely combined.
Stir in vanilla extract and maple extract.
Add egg and stir until well-combined.
In separate, medium-sized bowl, combine flour, cornstarch, baking powder, baking soda and salt.
Gradually (about ¼ of the mixture at a time), add the flour mix to the butter mixture and stir until completely combined.
Chill in refrigerator for at least one hour (may chill longer, up to 5 days).
Once dough is about 30 minutes from being ready, preheat oven to 375F and line a baking sheet with parchment paper.
Once dough has chilled, scoop into 2-Tablespoon (45g) sized scoops. Roll in or sprinkle lightly with granulated sugar and bake for 10-12 minutes.
Allow cookies to cool completely on cookie sheet. Do not put dough for following batches on hot cookie sheets, cookie sheets should always be room temperature or colder.