(adapted, originally inspired by a David Lebovitz recipe)
Preheat oven to 350. Line a 8” square baking dish with parchment paper or foil. If using foil, grease it with butter (you don’t have to line your pan if you are greasing it, but it makes it easier to get the brownies out after they are cooked).
Heat about an inch of water in a saucepan until simmering. Nest a heat proof bowl over top of the simmering water so that it does not rest IN the water. Place the chocolate and the butter in the bowl, and stir with a heat proof spatula until melted.
Remove from the heat and add the sugar. Once combined, stir in the eggs and vanilla, and mix until combined. In a separate bowl, whisk the cornstarch, salt and cocoa powder. Add to the chocolate mixture and stir well.
Pour into the prepared pan and bake 25-30 minutes. Cool in the pan. Brownies keep a few days at room temperature.