Melt chocolate in top of a double boiler over hot water. Remove from heat, add sweetened condensed milk, vanilla, salt and nuts. Stir until smooth. Turn into a wax-paper-lined 8-inch square pan or pour into a wreath shape onto a wax-paper-lined cookie sheet. Chill. When firm, slice.

Note: Black walnuts have a stronger taste the traditional English walnuts, so you may want to taste before deciding how much to add.