Preheat the oven to 325F. Melt the chocolate with the butter in the top of the double boiler over hot water until smooth. Cool slightly. Beat the eggs with the sugar in a large bowl until light. Slowly beat in the chocolate mixture. Stir in the vanilla. Sift in the flour, 2 Tbsp at a time, mixing well after each addition. Stir in the salt, sour cream and walnuts. Pour the batter into a greased 9 inch square cake pan. Bake until a toothpick inserted in the centre comes out fairly clean, about 25 to 30 minutes. The centre should be slightly cakey. Cool completely on a wire rack before cutting into bars. MAKES: ABOUT 20 BROWNIES