Combine sugar, half-and-half, and coconut milk in a 2- to 3-quart pan.

Stir over high heat until bubbles form at the pan edge (scalding, about 180°F), 5 to 8 minutes.

In a small bowl, whisk eggs to blend.

Whisk about 1/2 cup of the hot cream mixture into eggs.

Return egg mixture to the pan.

Stir over medium-low heat with a flexible spatula-scraper, scraping the pan bottom and sides thoroughly for even cooking, until custard thickly coats a metal spoon (about 190°F), 8 to 10 minutes.

Add vanilla to custard.

Nest the pan in ice water.

Stir custard often until mixture is cold, 10 to 15 minutes.

Pour cold custard through a fine strainer into a bowl, then pour mixture into an ice cream maker (1-qt. or larger capacity), or strain directly into the maker; discard residue.

Freeze according to manufacturer's directions.

As ice cream churns, stir coconut in a 10- to 12-inch frying pan over medium-high heat until toasted, about 4 minutes.

Pour toasted coconut from pan and let cool.

When ice cream is almost firm enough to scoop, add coconut and macadamia nuts.

Continue freezing until mixture is firm enough to scoop, dasher is hard to turn, or machine stops.

Serve softly frozen, or freeze airtight for later.