Preparation:
Fill a 1 pint (500ml (ish)) glass with half a pint of lager. Now take a shot glass that will hold a double measure. Fill the shot glass 3/4 full with Amaretto. Using the weird disc end of a bar spoon, float Bacardi 151 on top to fill the glass.

Drinking:
Holding the shot glass very carefully, set light to the 151, and then drop it directly into the lager as a depth charge. This will foam almost explosively. Attempt to down it in one.