In mixing bowl, combine oil and sugar. Add eggs, one at a time, beating well after each addition., Combine dry ingredients; add to batter and stir well. Fold in apples, walnuts and vanilla. Pour into a greased and floured 10 inch tube pan. Bake at 325 for 1 - 1/2 hours or until cake test done. Cool in pan 10 minutes; remove to a wire rack to cool completely. In the top a double boiler over simmering water, heat brown sugar, cream, butter and salt until sugar is dissolved. Cool to room temperature. Beat in confectioners sugar until smooth; drizzle over cake. Sprinkle with nuts if desired.