Using a peeler, grate the chocolate. Put the shavings into a small saucepan and add water. Warm for a few minutes on low heat, stirring continuously. Once the chocolate has melted, turn off the heat and add the star anise. Allow to infuse for 30 minutes and then remove the star anise.
In a large bowl, mix the milk and the yogurt or starter sachet, and then whisk until you obtain a smooth mixture. Add the chocolate sauce and mix well.
Pour the mixture into the bottles. Place them in the yogurt maker and cook in yogurt mode for 6 hours.
Once the programme is complete, close the bottles if you have not yet done so and place them in the refrigerator for at least 4 hours. Shake well before drinking.