Put all purpose flour, cocoa,baking soda, salt in a medium sized bowl. Mix using wire whisk. Set aside.
Melt butter in the microwave for 1 minute. Add in sugar and then egg. Mix using wire whisk and add vanilla extract. Mix again then add the dry ingredients to this wet ingredients.
Batter should be sticky but that's ok...
Fold in half of the chopped chocolate into the batter and transfer to the prepared pan.
Flatten butter and sprinkle the remaining half of the chopped chocolate on top. Gently press down.
Bake brownies from 25-30 minutes of until toothpick comes out clean.