Preheat oven to 350 deg f. In a small saucepan, melt butter; remove from heat. Stir in chocolate. Cool completely. In a small mixer bowl, beat eggs and vanilla. Gradually add sugar, beating until pale yellow. Blend in chocolate mixture. Gradually add flour and salt. Stir in nuts. Spread in a greased 20 cm square pan. Bake for 30 minutes or until done. Cool completely in pan. Cut into 5 cm squares. Makes 16 brownies.