Pour milk in a small bowl and sprinkle with gelatin. Let stand for 1 minute.
Bring cream, sugar and salt to a simmer in a medium saucepan over medium heat. Stir frequently until sugar is dissolved, about 2 to 3 minutes.
Reduce heat to low and whisk in chocolate until melted. Remove from heat and whisk in gelatin mixture until dissolved. Whisk in the buttermilk and vanilla.
Pour mixture into 4 serving glasses or ramekins. Refrigerate for at least 5 hours.
For the sauce, blend raspberries in a small bowl using an immersion blender. Pass through a fine mesh sieve and stir in icing sugar and liqueur. Serve over the chocolate panna cotta garnished with raspberries.