Ingredients

2 and 1/4 cups (281g) all-purpose flour (spoon & leveled)
1 and 1/2 teaspoons cornstarch
1 teaspoon baking soda
1/2 teaspoon salt
3/4 cup (1.5 sticks or 170g) unsalted butter, softened to room temperature
3/4 cup (150g) packed light or dark brown sugar
1/2 cup (100g) granulated sugar
1 large egg + 1 egg yolk, at room temperature
2 teaspoons pure vanilla extract
1 and 1/2 cups (270g) semi-sweet chocolate chips (plus extra for tops, if desired)

Instructions

Preheat oven to 325°F (163°C). Line 3 large baking sheets with parchment paper or silicone baking mats. (If you don’t have 3 baking sheets, bake the cookies in batches.)
Whisk the flour, cornstarch, baking soda, and salt together in a medium bowl.
Using a handheld or stand mixer fitted with a paddle attachment, beat the butter, brown sugar, and granulated sugar together in a large bowl on medium-high speed until combined and creamy, about 2 minutes. Add egg, egg yolk, and vanilla extract, then beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl as needed. Beat in the dry ingredients on low speed, then beat in the chocolate chips until combined. The dough will be thick.
Divide dough into 6 portions. Each will be a heaping 1/2 cup and weigh a little over 6 ounces. Shape each into mound, slightly flattening down the top. Place two on each baking sheet, at least 6 inches apart. Bake for 20-25 minutes or until edges and top are lightly browned. The center will look super soft, but it will set as the cookie cools.
Cool the cookie on the baking sheet for 15 minutes, then transfer to a wire rack to cool completely. As it cools, press a few chocolate chips into the top, if desired, for garnish.
Cookies stay fresh covered at room temperature for up to 1 week.

Notes

Make Ahead & Freezing Instructions: You can make the cookie dough and chill it in the refrigerator for up to 2-3 days. Allow to come to room temperature then continue with step 4. Baked cookies freeze well for up to 3 months. Unbaked cookie dough balls freeze well for up to 3 months. Normally you can bake frozen cookie dough balls straight from the freezer, but I recommend thawing these giant cookie dough balls prior to baking. Read my tips and tricks on how to freeze cookie dough.
Room temperature egg + egg yolk are best. Typically, if a recipe calls for room temperature or melted butter, it’s in good practice to use room temperature eggs as well. To bring eggs to room temperature quickly, simply place the whole eggs in a glass of warm water for 5-10 minutes. What to do with the extra egg white? Here are all my recipes using egg whites.
Will This Recipe Work for Regular Size Cookies? Yes! For 24 regular size cookies, measure out a heaping 1.5 Tablespoons of cookie dough per cookie and bake at 350°F (177°C) for about 12-13 minutes or until lightly browned on the sides.

Source : sallysbakingaddiction.com