Start by preparing the chocolate panna cotta:

1. Roughly chop dark chocolate, and add it to a saucepan along with heavy cream and milk. 
2. Over medium heat, bring to a simmer, stirring regularly to help melt the chocolate, for about 5-7 minutes. 
3. When the chocolate has melted and the preparation starts bubbling, add the agar agar.
4. Do not turn the heat down (the preparation should keep bubbling) and cook for 2 minutes, stirring dynamically and continuously with a whisk to help dissolve and cook the agar-agar. 
5. Remove from the heat, then, using an immersion blender, mix for 10 seconds to help smooth the panna cotta mixture. Try not to incorporate too much air while mixing: keep the immersion blender fully immersed (do not bring it to the surface).
6. Divide the hot chocolate panna cotta mixture among 4 heat-proof tumblers or ramekins.
7. Using a wooden skewer or toothpick, create slow circular motions in each tumbler to help eliminate potential remaining air bubbles. 
8. Allow to cool for 20 minutes at room temperature, then cover with cling film and place in the fridge overnight to set.

Make the berry compote:

1. In a medium saucepan, add the raspberries, sugar, and water.
2. Bring to a boil over medium-high heat, then cook for 1 minute, stirring with a wooden spoon.
3. Add the blueberries and cook for 2 more minutes.
4. Transfer the compote to a container and let it cool for 20 minutes. Cover with a lid or cling film, and store overnight in the fridge. 
5. Take the panna cotta and berry compote out of the fridge 10 minutes before serving to help loosen them up.
6. Top each panna cotta with berry compote and add some optional fresh berries on top. It’s ready! Enjoy immediately!