The Best Chocolate Chip Cookie

1 cup unsalted butter , melted and cooled at least 10 minutes (226g)
1 ¼ cup brown sugar tightly packed (250g)
1/2 cup sugar (100g)
1 large egg + 1 yolks (room temperature preferred)
1 ½ teaspoon vanilla extract
2 ¾ cups all-purpose flour (350g)
2 teaspoons cornstarch
1 teaspoon baking soda
3/4 teaspoon salt
1 bag semisweet chocolate chips
Alternate – for M&M mini cookies, use 150g brown sugar and 200g white sugar. Substitute 1/2 bag (or more) of mini M&M for chocolate chips.

Measuring ingredients by weight is recommended.
In a medium-sized bowl, whisk together flour, cornstarch, baking soda, and salt. Set aside.
Melt butter slowly, trying to keep it from separating.
Combine melted butter and sugars in a stand mixer bowl. Mix on medium speed until light in color and fluffy, this takes around 5 minutes.
Whisk egg and yolk together in a small bowl, then add egg to stand mixer. Mix on medium-low speed until egg is fully incorporated.
Add vanilla, mix until incorporated.
On medium-low speed, gradually add flour mixture to wet ingredients — stir just until flour is absorbed.
Stir in chocolate chips. Do not over work dough.
Cover dough and chill in refrigerator for 30 minutes.
Preheat oven to 350F
Form 35 gram dough balls and place onto prepared cookie sheets, placing at least 2″ apart.
Bake for 10-11 minutes
Leave on sheet for 2-3 minutes after removing from oven
Transfer cookies to cooling rack.