1For brownies: Preheat oven to 325 degrees. Line an 8 inch square pan or 9 inch pie plate with aluminum foil or parchment paper. Grease and flour liner and pan.
In a small bowl combine flour and baking soda. Set aside.
In a medium bowl melt chocolate and butter carefully in microwave. Stir until smooth. Whisk in sugar and then eggs. Beat in flour mixture. Spread evenly in prepared pan and top with chopped pecans.
Bake for 31 minutes or until a toothpick inserted in center of brownies comes out clean.
2For sauce: In a saucepan (stirring constantly)bring brown sugar, butter, and heavy cream just to a boil. Reduce heat immediately to a simmer and cook for 3 minutes. Stir in lemon juice or vinegar (which cuts the sweetness a bit). Serve over warm brownies with ice cream, if desired.