n a medium saucepan, bring the half-and-half, vanilla bean and vanilla seeds, and orange zest to a simmer over medium-high heat. Remove from the heat and discard the vanilla bean.
In a medium bowl, whisk together the egg yolks and sugar until thick and ribbons form, about 3 minutes. Gradually whisk in about 3/4 cup of the hot half-and-half, and whisk until well incorporated. Add the egg mixture to the saucepan with the remaining half-and-half and cook, stirring, over medium heat, until it forms a thick custard, about 5 minutes. Remove from the heat and strain into a clean bowl set in an ice bath to chill quickly. Add the orange flavored liqueur and stir to combine.
Cover with plastic wrap, pressing down on the surface to prevent a skin from forming, and refrigerate until cool, about 2 hours, or overnight.
Yield: about 2 1/2 cups