Thanks to the Washington Post
These gluten-free brownies taste of rich, unadulterated chocolate. At the lower end of the baking-time range (25 minutes), they are gooey and reminiscent of a molten lava cake. A few minutes longer in the oven and their crumb is more like a chewy brownie. Expect the chocolate chips to sink in the batter, which is why the foil sling is so important. We like that texture of crunchy chocolate at the bottom, but unless you line the pan, the slab of brownies will not release easily. Nuts are not included here, but you could scatter them, finely chopped, on the surface before baking. Make Ahead: The brownies can be stored in an airtight container at room temperature for up to 3 days, or in the refrigerator for up to a week. For long term cold storage, wrap them in plastic wrap and freeze, for up to 6 months.
Preheat the oven to 350 degrees. Press a long piece of aluminum foil into an 8-inch square pan to create a sling, leaving several inches of overhang on two opposite sides so you can use it to pull the baked brownie slab out of the pan. Grease the foil with cooking oil spray.
Melt the butter in a medium saucepan over low heat. Stir in the cocoa powder until thoroughly smooth and well incorporated.
Remove the pan from the heat; stir in the brown sugar, granulated sugar and vanilla extract, until smooth. Break the eggs into the saucepan, stirring until well incorporated. Add the cornstarch and salt, stirring until smooth, then fold in the chocolate chips. Pour the batter into the prepared pan, spreading it evenly into the corners.
Bake (middle rack) for 25 to 30 minutes, until the edges of the brownies are firm, the top is shiny and the center is just set. Let cool (in the pan) on a wire rack for 1 hour.
For easier slicing, you may then chill the brownie slab in the freezer for up to 1 hour. Use the foil sling to lift out the brownie slab before cutting into 16 pieces.