Here is recipe that makes delicious thick brownies with a chewy center and a beautiful shiny top. The secret is in how you handle the butter and sugar, plus a few special ingredients.
Preheat the oven to 350°F. Line an 8X8 light-colored metal pan with parchment paper and spray with cooking spray. Use a piece of parchment large enough to come up the sides of the pan and fold down the corners.
In a medium bowl, whisk together the melted butter, granulated sugar and brown sugar. Make sure the butter is just melted and not hot. If it is too warm, it will cook the eggs when added.
Whisk in the eggs, egg yolk, oil and vanilla extract.
Add the cocoa powder and flour and stir to combine. Stir in the sea salt, cornstarch and baking powder. Fold in the chocolate chips.
Use a spatula to spread the brownie batter into the prepared baking pan. Place the pan in the preheated oven and bake for 25-30 minutes. Test the brownies for doneness at 25 minutes. A toothpick placed in the center should come out with moist crumbs. If the toothpick is covered with really wet batter, continue to bake for a few minutes and test again. Do not cook until the toothpick comes out clean because the brownies will be overdone.
Allow the brownies to cool completely, then carefully lift use the parchment paper to lift the brownies out of the pan and cut.