Grease a cake tin of 7'' and keep it aside.
Sift wheat flour, cocoa powder, baking powder and baking soda at least 4 to 5 times.
Roughly chop dark chocolate, it eases its melting.
In a glass bowl, take milk, butter, dark chocolate and oil and put it in the microwave oven for 30 seconds or 1 minute till everything melts. After 30 minutes, check with a spatula as it may look as if it has not melted. If still hard then put it back in the microwave for another 30 seconds.
Add sifted flour to this liquid mix in batches.
The batter should be of ribbon consistency, meaning that it falls like a ribbon.
If not then adjust the consistency by adding little more milk.
Put the cake batter in the greased cake tin.
keep it aside and start preheating the oven.
Preheat oven at 170 degrees for 15 minutes.
Tap the cake tin to release air bubbles if any.
Bake it for 50 to 60 minutes till a skewer inserted comes out clean. This cake is baked at a lower temperature for a longer period.
Let the cake cool down and after 10 to 15 minutes, loosen the sides of the cake with a butter knife and invert it on a wire rack.
Let it cool completely. It will take an hour or so.
Once completely cool, you may serve as it is.
If want to go for frosting then keep it in an airtight container in the refrigerator at least for an hour or so.