Preheat the oven to 325 degrees F. If you plan to bake the brownies, and butter a 9-inch square baking pan. Otherwise, preheat a waffle iron. In a small bowl, mix together the flour, baking soda and salt. In a small, heavy saucepan, combine the sugar, butter and milk. Place over medium-high heat and bring to a boil, stirring until the butter has melted. Remove from the heat. Add the unsweetened chocolate and vanilla. Stir until the chocolate melts and the mixture is smooth. Place into a pan of cold water to cool the mixture to room temperature.
With an electric mixer, beat in the eggs. Gradually blend in the flour mixture until smooth.
(Spread evenly into the prepared pan if you are baking the brownies. Bake for 25 to 30 minutes until the center is just set and feels firm when touched. Cool completely before attempting to cut, these are very rich and gooey! Dust with powdered sugar and cut into squares.)
To make brownies in waffle iron: Drop rounded spoonfuls of the brownie mixture into the preheated waffle iron. Close the iron and cook for about 2 minutes until the brownies are done. Remove and cool on a rack. Dust with powdered sugar before serving, if desired.