Ingredients:

Semi sweet baking chocolate - 113 gms (4 oz or little more than 1/2 cup)
Butter - 113 gms (4 oz or little more than 1/2 cup)
Sugar - 1/3 cup
Eggs - 2
All purpose flour - 1/4 cup

Method:

Chop chocolate into small pieces and melt using a double boiler.
Chop the butter into small pieces too.
Once the chocolate melts completely remove it from heat and add in the butter.
Mix until the butter melts and mixes up smooth with chocolate.
In a mixing bowl, beat eggs and sugar until they turn light and fluffy.
Pour in the chocolate butter mixture and all purpose flour into the eggs and whisk until well incorporated.
Apply butter on the sides and bottom of the ramekins (small porcelain bowls/ moulds) and pour in the cake batter filling about 3/4th of the ramekin.
Preheat oven to 350°F or 180°C.
Bake at 350 deg F or 180 deg C for 10-15 mins.
Mine was perfect at 10 mins sharp.
Serve it warm with vanilla ice cream or enjoy it as it is :)

Tips:

Serve the cake just after you bake for a perfect flowing chocolate lava.
Once baked, allow the ramekins to cool down for just two mins and invert it on the serving plate.
Leaving it for long in the ramekin would not give you flowing lava.
Reduce the amount of sugar to 1/4 cup if your chocolate is sweet.

Note: Allow the batter to sit for ten mins and then bake the cake.

Recipe courtesy: 4th sense cooking