Whisk together coconut milk until smooth. Measure out 3 cups, reserve any remaining for another use or discard. 

Add 1 cup coconut milk to a medium bowl with a mesh strainer set on top. Set aside.

Add 2 cups coconut milk to a small saucepan with granulated sugar. Stir to dissolve sugar. Cook over medium heat until steaming. 

Continuously whisk yolks while slowly drizzling 1 cup steaming coconut milk mixture into yolks. Return to saucepan. Cook until mixture coats the back of a wooden spoon or rubber spatula. Pour through a mesh strainer into reserved 1 cup coconut milk. Stir in coconut extract, rum extract and pineapple juice. Stir to combine. Cool over an ice bath to room temperature. Cover and chill thoroughly. 

Churn according to manufacturer's directions. Transfer to a freezer safe container. Freeze until solid. 

Serve with optional toasted coconut flakes and pineapple slices.