- Heat half of the coconut milk and all of the gelatin in a small, heavy-bottomed saucepan over low-medium heat, whisking until the gelatin is dissolved, and bring to a gentle simmer. Add the butter and stir. 
- Remove from the heat, and add the remaining coconut milk, Erythritol, lemon zest, and vanilla extract. Stir until well combined. 
- Pour the mixture into four ramekins and place in the refrigerator for 2-4 hours to set. 
- Heat the berries in a saucepan until warm, and optionally add extra sugar-free sweetener. Mix until you get a smooth berry sauce. 
- Place the ramekins upside down to remove the panna cotta. Serve cold, topped with a sprinkle of lemon zest, fresh berries, and berry sauce.