In a large saucepan, whisk together the milk, 1 cup of the cream, egg yolks and sugar. Whisk in the lemon curd.
Over medium heat, whisk the mixture constantly, just until it starts to steam, but don't let it come to a boil. Remove from the heat.
Pour the mixture through a mesh strainer to strain out any bits of egg. Refrigerate until well chilled, preferably overnight.
Use an electric mixer to whip the remaining cup of heavy whipping cream until soft, thick peaks form. Fold the whipped cream and the limoncello or vodka into the lemon custard.
Churn the custard in your ice cream maker according to the manufacturer's instructions, until it's a soft serve consistency.
Transfer the ice cream to lidded ice cream container/s, and freeze until firm, about 6-8 hours.