Combine lemon zest, lemon juice and cordial in a small bowl and set aside.
Whisk egg yolks and sugar in a small bowl until pale then set aside
Add milk and cream to a medium saucepan and heat on high until simmering then remove from heat.
Scoop out around a cup of milk from the saucepan and slowly pour into the yolks - all the while whisking. Once combined, pour yolks into the saucepan of milk and continue heating on a low heat until it thickens enough to coat the back of a spoon.
Pour into an airtight container and stir in lemon mixture. Cool in refrigerator for at least 2 hours until completely cooled.
Prior to churning, pour milk mixture through a strainer if you don't like bits of lemon in your ice cream. Churn ice cream as per ice cream maker manufacturer's instructions.