Open the 2 coconuts. Extract the flesh from the shell, remove the brown outer layer, and cut into small pieces. Reserve the coconut milk in a separate cup.
Pour roughly 1 cup of water into a pan and bring to a boil over medium-high heat. Add 1 tablespoon sugar and 1 pack vanilla sugar. While stirring, slowly add the rum in small amounts as the sugar dissolves, about 2 minutes. Add the reserved coconut milk and return to a boil. Add the remaining 1 tablespoon sugar, remaining vanilla sugar pack, and coconut pieces. Reduce heat to low and simmer for 60 minutes, gradually adding rum as needed to maintain roughly 1 cm of liquid on top.
Let the mixture cool to room temperature. Pour the mixture into a large container and pour the remaining rum over the top. Seal tightly and let stand for 1 month.
Strain the liqueur through a fine sieve to remove all coconut pieces.
Serve the liqueur pure or dilute with cream in a 1:1 ratio if desired.
The strained coconut pieces are edible and taste good soaked in rum.