Add Sugar to the bowl with the yolks and stir- Set aside
In a Medium sauce pan, combine the milk and heavy cream- and heat on low while constantly stirring. Heat until small bubbles form at the edges- Do not boil
Turn the stove off, and stir in the egg yolk mixture, and then let cool
Add the Limoncello and Lemon curd- and blend until smooth and well-combined
Put the mixture into the Ninja Creami pint container and freeze for at least 24 hours
After 24 hours, remove the pint from the freezer, and remove the lid
Place the pint in the Ninja outer bowl with the paddle lid
Turn the Ninja Creami Ice Cream maker 'ON', and place the bowl in the locked-in upright position. Push the Gelato button.
Wait for the machine to finish its blending process, and remove the outer bowl and pint from the machine