Preheat the oven to 350°F (175°C). Line an 8×8 or 9×9-inch square pan with foil (prefer a metal one), then lightly spray or butter, and set aside.
In a small saucepan set over low heat, melt the butter, then add the sugar. Once the sugar is incorporated, add the chopped chocolate, stirring until smooth. Remove from the heat and beat for 2 minutes with a hand mixer or whisk. Add the eggs, one at a time, then the vanilla extract.
Using a mesh sieve (or a sifter), sift the cocoa powder and cornstarch into the saucepan, then add the salt. Stir together, then beat the batter vigorously for 1-2 minutes. I like to use a hand mixer for this on medium speed. Beat until the batter is smooth and shiny.
Pour the batter into the prepared pan and bake for 22-30 minutes or until the brownies are set in the center, taking care not to over-bake. Remove from the oven and let cool in the pan for 45 minutes before removing and slicing.
Notes
*I like to use 2 semisweet Ghirardelli baking bars, as they are 4 oz. each.-Fruit, nuts, chocolate chips/chunks, a sprinkle of sea salt, or a swirl of dulce de leche all make great additions to these brownies!STORE Fudgy Flourless Brownies in an airtight container at room temperature for up to 4 days. For longer storage, FREEZE them in a single layer, then transfer to a freezer-safe bag or container for up to 3 months.To REHEAT, microwave individual brownies for 15-20 seconds or warm them in a preheated oven at 350°F (175°C) for 5-10 minutes.