Place the half-and-half and clementine zest in a medium sized saucepan over medium heat. While that’s warming up, whisk together the egg yolks, sugar and clementine juice in a large bowl.
When the half-and-half has just started to simmer, turn the heat down to low add several ladles of it to the egg mixture while whisking. Pour the contents of the bowl back into the saucepan, using a spatula to scrape out all of the mixture.
Stir the liquid continuously over low heat until it has thickened slightly, about 5 minutes.
Remove from the heat and allow to cool for several minutes (continue stirring periodically).
Strain the ice cream base into a bowl or quart-sized measuring cup (discard the zest), and stir in the Grand Marnier and lemon juice. Cover with plastic wrap. Place the plastic wrap directly against the liquid to prevent a skin from forming. Chill until very cold, preferably overnight.
Use an ice cream machine and prepare according to manufacturer instructions.
Notes
Note: Tangerines or regular oranges my be substituted. The Grand Marnier is technically optional but adding it will result in softer ice cream that's easier to scoop straight from the freezer.