With an electric mixer, cream the butter and sugar.
Beat in eggs, one at a time. Stir in pumpkin, vanilla, lemon peel and lemon juice.
Gradually add dry ingredients, stirring until well blended. Stir in walnuts.
Drop by tablespoonfuls onto lightly greased cookie sheets and bake at 375 for 12-14 minutes. When cool, frost with Buttercream Frosting. Decorate frosted cookies with walnut pieces and candy corn if desired.
To make the frosting, beat together the butter and sugar. Stir in vanilla and cream; beat until smooth.