SPLIT CAKE INTO THIN LAYERS, spread with jam and half the apricot puree, and sandwich back together. Cut into bars, about 1-by-2-inches, and pack into a 2-quart serving dish, arranging oranges in and around cake. Pour Marsala over top, spread with remaining apricot puree and cover with custard. Cover and chill 2 hours. Whip cream with sugar until stiff. Frost on top of trifle and decorate with candied fruits, if desired.