In a medium bowl, combine egg yolks and sugar.
Beat until smooth. Set aside.
In a heavy saucepan, combine milk and cream.
Heat over medium low heat, stirring constantly, until mixture just starts to bubble around the edges.
Whisking constantly, pour a small amount of hot milk mixture over egg mixture.
Continue whisking and pouring until you've used about half of the milk mixture.
Add egg mixture to the saucepan with the rest of the milk mixture.
Return to medium low heat and cook until mixture coats a spoon, about 5 minutes.
Strain custard through a fine mesh sieve into a clean bowl.
Place in an ice bath to cool.
When custard is cool, whisk in Irish cream.
Pour into ice cream machine and process according to manufacturer's directions.