In a small saucepan, over medium low heat, simmer the pineapple juice to reduce down to 1/2 cup. Approximately 10-15 minutes.
Whisk the eggs, sugar, and salt together until thoroughly combined.
Whisking constantly, slowly pour the hot pineapple juice into the egg-sugar mixture.
Return the pineapple and egg-sugar mixture to the saucepan and cook over medium heat, stirring constantly.
Cook until the mixture thickens and coats the back of a spoon, about 2-3 minutes.
Remove from heat immediately. Stir in the cream and then the butter.
Pour the curd through a fine mesh strainer. Place in an airtight container and refrigerate until needed.
It will keep refrigerated, in an airtight container up to 4 weeks.