Heat the oven to 350°F. Lightly grease and line a mini loaf pan. I used a small 5.5 inch square pan but these will definitely work in a mini loaf pan. Set aside.
In a bowl, over a double boiler on medium to medium low heat, melt together the chocolate, butter, and cocoa, stirring with a spatula until melted and smooth. Set aside to cool.
In a medium bowl, whisk together the sugars, egg, and vanilla until lightly pale. Whisk in the slightly cooled chocolate butter mix.
Use a spatula to gently mix in the flour and salt, barely incorporating it and being careful not to over mix. One to two flour streaks are okay.
Scoop into the prepared pan and spread out. Bake for 20-24 minutes or until a toothpick in the middle comes out clean. Cool on a wire rack before slicing and enjoying!