In a large saucepan combine 750 ml (3 cups 2 TBSPs) milk, vanilla extract and all the sugar. Cook over medium heat, stirring occasionally, until the sugar dissolves and milk begins to simmer.

Meanwhile, combine the rest of the milk with powdered chocolate and cacao. Whisk until smooth.

Add the chocolate mixture to the milk and let simmer for about 20 minutes, whisking occasionally.

Remove saucepan from stove and let cool to lukewarm. Whisk in the rum. Strain the chocolate liqueur and pour into prepared bottles.