Cream shortening and sugar together in mixing bowl. Into a separate container, sift together flour, salt, soda, and cocoa. Add to creamed ingredients alternately with buttermilk; blend well. Stir in rolled oats and chopped nuts. Bake in a greased and floured 13x9x2-inch baking pan. Bake at 350° for 35 minutes, or until a wooden pick or cake tester inserted in center comes out clean. Cool in pan on rack. Spread with Peanut Butter Frosting, below.
Peanut Butter Frosting
6 tablespoons peanut butter
1/3 to 1/2 cup cream
1 1/2 teaspoons vanilla
1 1/2 cups sifted confectioners' sugar
Blend together the peanut butter, cream, and vanilla. Add sifted confectioners' sugar, adding more cream or confectioners' sugar if necessary for spreading consistency. Spread a thin layer of icing over cooled cake.