Preheat your oven to 350°F. Lightly grease a 9" x 13" pan. Melt the butter in a medium-sized saucepan. Add the brown sugar, and stir until the mixture is smooth., Remove the pan from the heat, pour the butter-sugar mixture into a medium-sized bowl, and allow it to cool to lukewarm. Add the remaining ingredients, except the chips and nuts, stirring to combine. Fold in the chips and nuts., Spread the mixture evenly in the pan, and bake the brownies for 30 to 35 minutes, until they're light brown on the edges and top. Remove them from the oven, loosen their edges with a table knife, and cool completely before cutting.