In a large bowl, whisk together the flour, cornstarch, baking powder, baking soda and salt. Set aside.
In a separate large bowl, beat together the butter and sugar until creamed (about 2-3 minutes).
Beat the egg, sour cream, vanilla extract and almond extract into the butter mixture. Turn off the mixer and scrape down the bottom and sides of the bowl a few times.
With the mixer on a low speed, beat the dry ingredients into the butter mixture. Mix together until evenly combined and there are no lumps. The dough will be thick.
Cover the bowl and refrigerate for at least 1 hour or up to 48 hours.
When ready to bake, preheat the oven to 350℉ (180℃). Line 2 cookie sheets with parchment paper or baking mats.
Scoop the dough into balls with about 1½ tablespoons of dough each (I recommend using a cookie scoop). Place the dough balls about 2½ inches apart on the lined cookie sheets.
Bake 1 sheet at a time in the middle of the preheated oven. They will bake for about 12-14 minutes. Once finished, the tops should look set and the shouldn't feel doughy if you lightly press your finger onto the top of the cookie.
Cool the cookies on the cookie sheets.