Preheat oven to 350 degrees. Prepare double boiler by placing 1-2 inches in the bottom saucepan and bringing to a simmer. Line an 8 inch square baking pan with parchment paper and set aside.

In a medium mixing bowl add flour, baking powder, salt and cocoa powder, stir to combine well.

When the double boiler is ready, add chopped chocolate and butter, stirring often with rubber spatula until completely melted and well blended.

Remove from heat and add brown sugar to the chocolate, stirring until dissolved and well combined.

Add eggs and vanilla and whisk to combine.

Stir the flour mixture into the chocolate mixture and stir well.

Add 2-3 tablespoons of cocoa powder to a bowl, add the squares of chocolate bar and toss gently to coat, remove the chocolate and fold it and the chopped pecans (if using) into the brownie batter.

Transfer to a parchment lined square baking pain and smooth down with spatula. You an add a few broken pieces of chocolate bar and a few chopped nuts to the top of the batter, pressing down slightly. Bake for 35 to 45 minutes, until toothpick comes out with just a few crumbs.

Remove from heat and allow to cool completely before cutting into squares.