Take a non-stick pan on the gas with minimum flame and melt some ghee in it. Now add milk and sweetened condensed milk to it along with the ghee and stir it for one minute till it heats up.
Sieve the milk powder and cocoa powder together in a mixing bowl. This ensures that they blend well together and the cocoa powder has no lumps in it. Pour the powder mixture into the pan that we have heated up and keep on stirring continuously. Make sure that the mixture has no lumps in it.
Pour the vanilla essence and cook it for five to six minutes over a minimum flame.
Take the warm dough on the plate and spread it with a thin layer of ghee. Leave it there to cool down for five minutes. Once the mixture cools down enough to be handled, take a lump and, with the greased fingers, knead it for one minute. This gives it a crack-free dough ball with a glossy chocolate skin.
While the chocolate dough is resting, quickly whip up the white mava filling using extra milk powder, condensed milk, ghee and cardamom in the same pan on a low flame for two to three minutes. It should become a small hard ball.
Lightly grease the modak mold using a little bit of ghee and clamp it. Press some warm dough from the chocolate dough into the bottom opening and along the sides to create a thin shell. Add a small ball of white filling to the inside if you wish to. Now cover the bottom with the rest of the chocolate dough and press it in tightly. Open the modak mold.