In a separate, medium-sized bowl, whisk together flour, cornstarch, baking soda, cream of tartar, and salt.
3 ½ cups all-purpose flour, 1 teaspoon cornstarch, 1 teaspoon baking soda, ½ teaspoon cream of tartar, ½ teaspoon salt
With mixer on low speed, gradually add flour mixture to your wet ingredients until completely combined.
Using a spatula or with your mixer on low-speed, stir in 1 ½ cups of the chocolate chunks/chips, and pause to scrape down the sides of the bowl so that chocolate is well incorporated.
2 cups semisweet chocolate chunks or chocolate chips
Scoop dough by 1 ½ Tablespoon-sized balls and gently roll between your palms for a smooth ball. Place on cookie sheet, spacing at least 2" apart, and bake on 350F (175C) for 8-10 minutes. Cookies may still seem soft in the centers but will continue to bake on the cookie sheet as they cool.
Within one minute of removing from the oven, gently press remaining chocolate chunks/chips into the tops of each cookie. Allow cookies to cool on baking sheet for at least 10 minutes.