Preheat oven to 325 degrees. In a small bowl, combine flour, baking soda, and salt; set aside. In a small saucepan, place butter. Completely melt butter over medium heat. Add 6 ounces chocolate chips to melted butter. Stir until chips melt and mixture is smooth. Add vanilla extract to butter and chocolate mixture. Stir well and remove from heat. Add sugar to melted butter, chocolate, vanilla mixture in saucepan. Combine. Transfer to a large bowl. Add eggs, one at a time, beating well after each addition. Gradually blend in flour mixture. Stir in remaining 6 ounces of chocolate chips and the nuts if you choose to add them. Spread into a greased 9-inch-square baking pan. Bake 30 to 35 minutes. For gooey brownies that go great with vanilla bean ice cream and berries, cool only for 10-15 minutes. Otherwise, cool completely. Cut into 2 1/4-inch squares or whatever size you like!