Toast macadamia halves at 325°F for 8–10 minutes until golden. Cool completely on a plate.
Heat cream, milk, and salt in a heavy saucepan until steaming. Do not boil.
Whisk egg yolks and sugar until pale and slightly thickened, about 90 seconds.
Temper: ladle ½ cup hot cream into yolks while whisking constantly. Repeat with a second ladle.
Return to saucepan. Cook over medium-low, stirring constantly, to 170–175°F (nappe).
Remove from heat. Stir in rum, curaçao, orgeat, and vanilla.
Strain through a fine-mesh sieve. Press plastic wrap onto surface. Chill 4 hours or overnight.
Churn 20–25 minutes until soft peaks form.
Add cooled macadamia halves during final 2 minutes of churning.
Transfer to container. Press plastic wrap onto surface. Freeze 4 hours.