In a wide bowl take the butter and cream well. Next, add the condensed milk and continue beating till it is creamy.
Take the chocolate and melt in the microwave for 30 secs until it melts and add to the condensed milk.
Continue creaming until mixed well.
Now, add the instant coffee powder. You can mix 2 tbsp of hot water to the instant coffee powder and melt well.
Add vanilla essence and beat to combine.
Sift the flour a couple of times and keep it aside.
Now, add the flour in three batches alternating with milk to the condensed milk bowl.
Repeat until you complete both milk and flour. Beat until combined.
Preheat the oven to 185 C. Grease a 9 inch baking round tray and line it with a parchment paper.
To the mixing bowl, finally, add the Baking Soda and vinegar and gently fold in using a spatula.
Immediately transfer to the lined baking tin and tap it down so that it settles well.
Bake at 185 C for 35 to 45 minutes or until a toothpick / sharp knife inserted comes out clean.
Loosen the sides of the cake from the tin using a knife.
Flip it on to a wire rack and remove tin and paper.
You can frost it with Dark Chocolate Ganache or wrap it with cling film to use it later.