Place the half and half, ¼ cup of the sugar, the nutmeg, lemon zest, orange zest and vanilla bean seeds and pod (now empty) in a small pan and cook over low heat, whisking from time to time, until it is warm, about 175°F.
Place the egg yolks, ¼ cup of the sugar and the salt in a small metal bowl and whisk until completely mixed.
Add ¼ cup of the warm half and half mixture to the eggs, whisking all the while. Continue adding half and half to the eggs, ¼ cup at a time, until you have added about ½ cups. Slowly, whisking all the while, return the now half and half and egg mixture to the remaining half and half mixture in the pan and continue cooking until it just begins to thicken or reaches about 185°F. Do not allow the mixture to boil.
Pour through a medium fine strainer into a metal bowl, discard the solids and set aside until it reaches room temperature.
Add the Amaretto, Anisette and Grand Marnier and stir well.
Cover and refrigerate at least 8 hours or overnight.
Transfer to an ice cream maker and proceed according to the manufacturer’s instructions.