Bring the milk very slowly up to boiling point with the cinnamon stick or vanilla pod — one or the other, not both. Pop the pared lemon peel in the pan and let them infuse for about 5 minutes off the heat. This way the milk will absorb the flavours.
Meanwhile, whisk together the egg yolks and caster sugar. Strain the milk and pour it bit by bit into the egg yolks and sugar. Return this