Measure all ingredients and bring to room temperature. Melt the chocolate in the top of a double boiler over hot water. Line the bottom of the loaf pan with brown paper. Grease the paper and the sides of the pan with butter and dust the whole interior lightly with flour.
Beat the butter well and gradually add the sugar until the mixture is creamed and very light and fluffy. Add the eggs one at a time, beating well after each addition. Beat in the vanilla. Sift the flour, salt, baking powder, and soda together. Add the sifted flour mixture to the butter mixture in three parts, alternating with the buttermilk. Stir the batter well after each addition until smooth. Add the melted chocolate and toasted nuts and fold just enough to mix evenly. Pour into the lined loaf pan.
Place in the middle level of the preheated oven and