Preheat the oven to 350F then line a baking sheet with parchement paper and set aside.
Cream the butter, brown sugar, and granulated sugar until light and creamy.
Add in the egg, egg yolk, butter flavoring, vanilla flavoring, maple flavoring, and mix until combined.
Add in the flour, corn starch, cream of tartar, baking powder, and salt, and mix just until the flour mixture disappears.
Using a large cookie scooper, scoop out 12 equally sized cookie dough balls, roll them in between the palm of your hand and using a chop stick, slightly press down on the cookies to make the waffle indentations (as shown on the photo).
Then freeze the cookie dough balls for 15 minutes before baking in the preheated oven for 14 minutes. Let the cookie cool down on the baking sheet for another 15-20 minutes before transferring to a cooling rack to cool fully.