Sieve together flour, cocoa powder, baking powder and baking soda few times. Grease and line a microwavable bowl, approximately 9 x 9 inches in size.
Cream together butter, salt and sugar until the mixture is fluffy. Add the condensed milk and vanilla extract, and mix well. Now slowly fold in the flour mix into the batter while alternating with the 1 cup of buttermilk. Mix well when finished
Bake the mixture on high (100% power) for exactly 6 minutes. Let the cake rest in the microwave oven for a few minutes, and let it cool for 10 minutes before trying to unmould it.
This can also be baked in the OTG at 180°C for 30 minutes