Preheat oven to 350 degrees.

Grease a 9"x13" pan.

Melt the butter in a saucepan over medium heat.  Once melted, remove pan from heat.

Add chopped chocolate and allow to melt from heat of butter.  Stir to smooth and allow to cool slightly.

In a mixing bowl, add brown sugar.  Mix in eggs, one at a time, using a spatula or whisk to mix.  Dissolve brown sugar until no clumps remain. 

Stir in granulated sugar.  Add vanilla and mix well.

Stir in cooled chocolate mixture and mix well.

Fold in salt and flour, just to combine where no white is showing.

Scrape batter into prepared pan.

Bake for 30 minutes.  Use the toothpick test in the middle of brownies looking for a clean toothpick.  Top should be crackly.

Cool completely.

For best cutting results, refrigerate at least 90 minutes.  Using a plastic knife to cut will result in best cuts.

These freeze really well but keep for several days if wrapped.