Preheat oven to 375°F. Line 2 baking sheets with parchment paper and set aside.
Using a hand mixer, cream butter until smooth, about 2-3 minutes. Add the sugars and beat until smooth, about 2 minutes. Beat in the eggs and vanilla until smooth, about 1 minute.
1 pound unsalted butter, 1½ cups light brown sugar, 1½ cups dark brown sugar, 1 cup granulated sugar, 4 large eggs, 2 teaspoons pure vanilla extract
Into a large bowl, sift together the dry ingredients. Slowly mix the dry ingredients into the wet mixture. Fold in the chocolate chips.
3½ cups all-purpose flour, 1½ teaspoons kosher salt, 2 teaspoons baking soda, 1½ cups semisweet and milk chocolate chips
Drop 2 tablespoons of dough per cookie onto the prepared baking sheets; space the dough balls at least 2 inches apart to allow for spreading. Plan on approximately 6 cookies per sheet.
Bake until golden, 9-11 minutes. Remove cookies from the oven.
Let cookies stand on the baking sheets for 10 minutes before removing to a cooling rack to finish cooling. Repeat with remaining dough until all cookies have been baked.