Preheat oven at 350F for about 10mins.
Grease a baking dish with butter and flour, keep aside.
Sieve together dry ingredients - cake flour, baking powder, baking soda, cocoa powder and keep aside.
Take condensed milk and butter and beat till well mixed.
Alternately add orange juice and dry ingredient, a little at a time and mix gently.
Bake at 350F for about 40-45mins till a tooth pick inserted in the center comes clean.