In a small bowl, combine gelatin with cold water to cover and allow to set, about 2 minutes.
In a medium saucepan over medium heat, combine whole milk and heavy cream. Add sugar and vanilla extract. Stir constantly for 3 minutes until the sugar is dissolved.
Remove saucepan from the heat and add the gelatin. Strain the mixture through a sieve into a bowl. Set the bowl inside a larger bowl of ice water and allow to cool to room temperature, stirring occasionally. When the mixture is cool, stir in buttermilk until incorporated. Transfer the mixture into small dessert dishes or ramekins. Cover lightly with plastic wrap and refrigerate to set, about 2 hours.
To serve: In a small bowl, combine raspberries, sugar and lemon zest. Remove panna cotta immediately before serving, and top with raspberries.
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