Crush the (desired amount of the) liquorice stick, place the crushed pieces in a sauce pan together with the cream and the milk. Bring slowly to an almost-boil, stirring occasionally, until most of the liquorice has melted and the cream has taken on a nice, brown colour.
Whisk together the egg yolks and the sugar.
Blend the egg yolk-sugar mixture with the hot liquorice cream. Stirring incessantly, bring the blend towards a boil, taking the sauce pan off the heat once the first bubble breaks the surface of the ice cream base [the more scientifically minded makes sure that the pasteurising stage of about 82-84º C /189-183ºF has been reached; the so-called nappe stage].
Once cooled down, let the ice cream base chill in the refrigerator for at least a few hours. Transfer to an ice cream machine and churn according to instructions.
Store in a freezer-safe container and cover with plastic film and a lid.