Grease and dust your cake tin with some butter and flour.
In a bowl, whisk together butter, condensed milk and vanilla essence.
Combine baking powder and whole wheat flour in another bowl.
To a 5 liter pressure cooker (or bigger) add 1-2 cups salt. Place a wire rack or a perforated plate over it. Heat the cooker on medium flame. Keep the lid on it but remove the whistle.
Add 1/2 the flour and some water. Mix gently. Add the remaining flour and water and make a smooth and thick batter.
Pour the batter into the prepared cake tin and keep this tin in the hot cooker carefully. Keep flame on medium for first 2-3 minutes then switch it to low and bake for 35 minutes.
After 35 minutes check by inserting a knife. If it comes out clean then your cake is done.
Serve with a little chocolate syrup poured on top of cake pieces. Served best when warm!