Sheet Pan Chocolate Chip Cookies

• Start by melting 1 1/4 cups (2 1/2 sticks) of unsalted butter in a large, microwave-safe bowl and cover with a moist paper towel. Heat it in 20-second intervals until it's melted, then set aside to cool for about 10 minutes (this prevents the butter from melting the chocolate chips).
• While the butter cools, preheat the oven to 350°F/175°C and grease and line a 13x18-inch half sheet pan with parchment paper.

  It's important you line the pan with parchment paper, or else it can be difficult to remove the cookie squares once they're cut, and you can end up with little bits of metal scrapings from the pan on your cookies (this happened to me once!).
• Add 1 1/2 cups packed brown sugar, and 1/2 cup granulated sugar into the melted and cooled butter (it should still be liquid, but not hot to the touch). Whisk the ingredients together by hand for about a minute or use an electric hand mixer and mix on a medium-low speed, until the mixture is smooth, and no lumps remain. It should become lighter in color as it's mixed.
• Then mix in 3 large eggs and 1 Tbsp vanilla extract until fully incorporated.
• Next, add 3 1/4 cups flour, 1 tsp cornstarch, 1 tsp baking soda, and 1 tsp fine salt into the mixture and stir together with a wooden spoon or spatula. Mix until no visible streaks of flour remain. Scrape the bowl's sides and bottom as needed to ensure everything gets properly mixed together. The dough will be soft/sticky, but that's how it's supposed to be!
• Then fold in 1 1/2 cups of chocolate chips or chunks of your choice (save the last 1/2 cup to sprinkle over the top of the bars).
• Scoop the dough into the prepared pan and spread it into an even layer using a rubber spatula or offset spatula. Sprinkle the remaining 1/2 cup of chocolate chips on top of the dough.
• Bake the tray for 22-26 minutes, and rotate the pan halfway through to help it bake evenly. The cookie sheet is ready when the edges just start to brown but the centers still look slightly puffy/under-baked. The cookies will continue to bake on the sheet and firm up once removed from the oven, so it's always best to err on the side of under-baked!
• Place the cookie sheet on a wire rack to cool fully. I like to add a garnish of flaky sea salt while the cookies are still warm. Then cut the sheet into slices with a butter knife and enjoy! One sheet can be cut into about 54 2x2-inch squares.
• These cookies can be stored in an airtight container at room temperature for up to 3 days.