Setup your cooker with baking tray for pre-heating on medium flame for about 10-15 minutes.
If you're using bourbon biscuits, separate the cream from it. Grind the biscuits (only) to a fine powder.
In a double boiler, put around 100 gms of chocolate for melting. Keep 2-3 pieces aside for later.
In a bowl, mix the biscuit powder and melted chocolate well. Add1 cup milk gradually while mixing the ingredients into forming a smooth shiny liquid batter.
If you don't have readymade moulds or paper cups, take some aluminium foil and make a cup shape using back of a glass. Make it a double layer cup and gently fold the sides that it becomes stiff and shapes well into moulds.
Pour a little more than ¼ cup batter into the cup and add a piece of chocolate gently, do not drown the chocolate. Now, add a little more batter very gently just to top coat the chocolate piece.
Place the cups with batter onto the baking tray in pre-heated cooker and bake it for about 5 minutes. Make sure to check it after 3 minutes so that it is not overbaked. It should remain soft on the inside.
Remove from the cup. If you used aluminium foil cup or paper cup, you can tear it carefully to remove the cake. Plate it and cut to see the lava flowing out gracefully. Enjoy!