Combine oil and sugars in a large mixing bowl. Add eggs, one at a time, beating well after each one. In a separate bowl 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 in a preheated 325 degrees F oven for 1 to 1 1/2 hrs or until it tests done. Cool in pan 10 min. Remove to a wire rack and cool completely.
In the top of a double boiler over simmering water, heat brown sugar, cream, butter and salt till sugar is dissolved. Cool to room temperature. Beat in confectioners' sugar until smooth. Drizzle over cake. Sprinkle with nuts if desired.