Place the milk and condensed milk in a small heatproof bowl and warm it up in the microwave for 30 seconds. Stir together and reserve.
In another heatproof bowl, place the chocolate and melt it in the microwave in 30-second intervals, mixing in between.
Once the chocolate is completely melted, pour the milk onto it. Using a rubber spatula, mix at the very center of the bowl. Slowly but surely, there will be a swirl of ganache forming at the center and slowly increasing in volume until everything is completely mixed and smooth. Reserve.
As soon as the cake comes out of the oven, poke holes in the cake and immediately pour the chocolate sauce on top. Spread it evenly.