Preheat oven to 350°F. Parchment paper should overhang the two long sides of a 9" x 5" loaf pan by two inches.
Step 2
Put butter and unsweetened chocolate in a large microwave-safe bowl. Heat at half-power for 30 seconds until butter and chocolate melt when swirled. Stir smooth. Allow to cool slightly.
Step 3
Mix chocolate powder and sugar. Stir in egg and vanilla. Stir add flour and salt until mixed. Place batter in pan and spread evenly.
Step 4
A pick inserted into the center should come out with a few moist crumbs after 22–26 minutes.
Step 5
Let brownies cool completely in the pan on a wire rack. Lift brownies from pan to cutting board with overhanging parchment paper. Cutting into bars.