On a chopping board, soak the brown sugar cubes with a dash of angostura bitters on each. Put the sugar cubes into a 1½ litre jug, add the still mineral water, a dash of monkey shoulder whisky from a measured 500ml, then gently muddle the mix (using a rolling pin) so that the sugar is almost completely dissolved.
Add half of the remaining whisky and about 10 to 15 ice cubes and stir gently. Add the rest of the whisky, a handful more ice cubes, then stir. Strain the drink into 10 old-fashioned glasses, already filled with ice cubes. Squeeze an orange peel twist over each glass, then drop it into the glass.