1 ½cups(255g)chocolate chipsoptional, I did a mix of semisweet chocolate chips, milk chocolate chips, and butterscotch chips
Instructions
Preheat oven to 350F (175C) and line a 9x9 metal baking pan with parchment paper or grease and flour the sides and bottom of the pan.*
Combine butter and sugars in a large bowl and stir until well-combined.
1 cup butter, 1 cup light brown sugar, ½ cup sugar
Add eggs and vanilla extract and stir well.
2 large eggs + 1 large egg yolk, 1 ½ teaspoons vanilla extract
In a separate bowl, whisk together flour, cornstarch, baking powder, salt, and cinnamon (if using).
1 ¼ cup all-purpose flour, 2 teaspoons cornstarch, ½ teaspoon baking powder, ¾ teaspoon salt, ¼-½ teaspoon ground cinnamon
Gradually add dry ingredients to wet until completely combined.
Add oats and chocolate chips and stir until well combined.
3 cups old fashioned rolled oats, 1 ½ cups chocolate chips
Spread cookie dough evenly into prepared baking pan and bake on 350F (175C) for 35-40 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Video
Notes
*A glass baking pan will work for this recipe instead but it will likely take longer to bake.