Place the milk and cream in a saucepan. Scrape in the vanilla seeds and add the bean. Bring to the boil, then turn off the heat and set aside for 10 minutes to infuse. Place the egg yolks, sugar and vanilla extract in the bowl of an electric mixer. Beat until pale. Carefully pour the milk over the egg mixture, then return to a clean saucepan.
Cook over a low heat, stirring, for about 5 minutes until it is slightly thickened and coats the back of a wooden spoon.
Stir through the macadamia butter, set aside to cool then refrigerate for 30 minutes. Place in a plastic container in the freezer until frozen on the edges. Remove from the freezer, beat with an electric beater then re-freeze. Repeat this process 2 more times. (If you have an ice-cream machine, churn the mixture according to manufacturer’s directions).