Step 1

Adjust the oven rack to the lower third position, just below the center of the oven, and heat the oven to 350°F. Line an 8x8-inch pan with parchment paper or aluminum foil, leaving a 1-inch overhang on all sides. Spray lightly with nonstick spray and set aside.

Step 2

In a medium heatproof bowl set over a pot of barely simmering water, melt the chocolate and butter, stirring constantly until the mixture is smooth. You can also microwave in 30-second intervals, stirring between each one.

Step 3

Remove from heat and whisk in the cocoa powder. Set aside to cool slightly.

Step 4

In a separate bowl, whisk the egg and sugar, vanilla, and salt together until well combined and the mixture is frothy.

Step 5

Add the warm chocolate mixture and whisk until well combined.

Step 6

Add the flour and use a silicone spatula to fold the batter together until no visible streaks of flour remain.

Step 7

Spread the mixture evenly into the prepared pan and bake for 20-25 minutes or until a toothpick inserted into the center comes out with a few moist crumbs clinging to it.

Step 8

Cool on a wire rack to room temperature, about 2 hours, then remove from the pan and cut into squares.