Preheat oven to 350°. Cream butter and sugar. Sift together flour, salt, baking soda and spices; add to creamed mixture. Add eggs, 1 at a time, beating well after each addition, and molasses. Blend in coffee. Spread in a 15x10x1-in. baking pan.
Bake 20-25 minutes. Cool. For frosting, cream butter and cream cheese; add confectioners' sugar and vanilla. Spread over bars. If desired, top with nuts.