Preheat the oven to 350F (180C) degrees. Line cookie sheets with parchment paper or silicone baking mats.
Whisk together the flour, cornstarch, baking soda, baking powder and salt. Set aside.
In a separate large bowl beat the butter, brown sugar and granulated sugar until you no longer see chunks of butter.
Beat in the egg and vanilla extract.
Add the flour mixture into the butter mixture. I typically do a few stirs by hand first. Then beat together, starting with the mixer on a low speed and slowly increasing to a medium speed until the flour mixture is incorporated.
Stir in the chopped berries and chocolate chips.
Scoop the dough into balls. I like using a cookie scoop for uniform cookies. For large cookies (like those pictured) form the dough into balls with about 3 tablespoons of dough each. You should get 11-12 cookies. For smaller cookies, form the dough into balls with about 1 - 1.5 tablespoons of dough each. You'll get about 22 cookies. Place cookies 2 inches apart on the cookie sheets.
Bake 1 sheet at a time on the middle rack of the oven. Large cookies will take about 12-14 minutes to bake. Small cookies will take 9-11 minutes.
Cool on the cookie sheet for at least 10 minutes, the transfer to a cooling rack to continue cooling. Optionally, dot the top of each cookie with a few extra chocolate chips.