Preheat oven to 325 degrees. Butter a 9-by-13-inch cake pan. Cut a piece of waxed paper to fit the bottom, and press it onto buttered surface. In a large microwave-safe bowl, combine butter, brown sugar, and chocolate. Microwave on high for 1 minute; stir. If the chocolate is not softened, continue to microwave at 10-second intervals, removing before completely melted.
Beat the eggs and vanilla into the melted chocolate with a wooden spoon. Beat in the flour and salt. Pour into prepared pan, and smooth the top. Bake until a toothpick inserted in the center comes out almost clean, 35 to 40 minutes. Let cool.
Run a knife around the edge of the pan. Turn the brownie cake out onto a baking sheet, and flip over onto a work surface. Cut out the brownies with a 2 1/2-inch heart-shaped cookie cutter. Dust with cocoa if you like. Form the scraps into 1-inch balls, and roll them in the coating of your choice.