In a bowl, whisk the flour, and cocoa powder together until well combined.
Set aside until needed.
In another bowl, cream the butter and sugar with a whisk until it comes together. You don't need an electric beater, just do this step by hand until the butter and sugar are well incorporated
Now add milk,baking powder, baking soda, yogurt and vinegar into this and mix properly until the mixture is a bit fluffy.
Add the vanilla extract mix gently again.
Now add the flour mixture in two additions, folding gently after each addition. Do not over mix at this stage, just mix until you don't see any traces of flour remaining and the batter is lump free (small lumps should be okay, they will disappear on baking)
Grease the cake tin and pour this batter in a cake tin.
Tap the cake pan firmly on the kitchen counter a couple of times to remove any air bubbles in the batter
Preheat the pressure cooker by placing the plate or tray at the bottom of the pressure pan and closing the lid (no water needed, no gasket needed on the lid)
Heat on medium flame for about 2 minutes until the cooker is hot
Gently lower the cake pan with a pot holder into the pressure pan
Close the lid and keep the flame low to medium
Cook for about 45-50 minutes until the a toothpick inserted into the cake comes out clean. The cake will also leave the sides of the pan, which is a good indication that it's cooked.
Remove from inside the cooker and cool for 10 minutes in the cake pan.
Then, gently invert onto a cooling rack or plate and cool the cake completely & serve.
