Preheat the oven to 350 and prepare a cookie sheet with parchment paper. Set to the side.
Combine the flour, cornstarch, baking soda, and salt in a small bowl. Set to the side.
Using a hand or stand mixer with a paddle attachment, cream the butter with the sugars until light and fluffy, about 2-3 minutes. Add the egg and the extracts and mix until smooth. Scrape down the sides of the bowl as needed.
Gradually add the dry mixture to the butter mixture. Mix on medium-low until smooth.
Fold in the white chocolate chip and peppermint chips. Mix in with the mixer or a rubber spatula.
Form the cookie dough into balls using a cookie dough scoop. Top the cookie dough balls with extra white chocolate chips and peppermint chips, if desired.
Bake the cookies in the oven for 10-12 minutes, until the edges are golden brown. Let the cookies cool slightly on the cookie sheet before moving to a cooling rack.
