Preheat oven to 350~. Over low heat, melt butter and chocolate. Remove from heat. Stir in flour and vanilla. With mixer, whip eggs and sugar until mixture resembles a yellow ribbon. Blend in chocolate mixture on slow speed. Stir in walnuts. Spread batter into a greased 9x13" and a greased 8" square pan. Bake 35 minutes for large pan: 30 minutes for small pan. Makes 3 1/2 dozen. Noah's Ark is a popular restaurant in the St. Louis area.