Sift together flour, cocoa, baking powder, baking soda, cinnamon and cloves. Set aside.
In a large mixing bowl, combine butter, oil and sugar. Add eggs and mix well. Stir in zucchini and vanilla. Add dry ingredients alternatively with sour milk. Stir in chocolate chips.
Turn into greased 9 X 11 inch cake pan. Bake at 350 degree oven for 35 to 40 minutes or until centre springs back when pressed with fingertip.
Frost with basic buttercream icing, if desired. Cut into squares.