- In a bowl, sprinkle the gelatin over the water. Let bloom for 5 minutes. Set aside.
- In a saucepan, gently heat the cream, milk, sugar, and lemon zest, stirring until the sugar has dissolved.
- Add the gelatin mixture and stir with a whisk until completely dissolved. Strain.
- Use eight 125 ml (½ cup) ramekins or jam jars. For easy unmoulding, rinse the jars or ramekins with cold water. Drain quickly without drying and add the panna cotta mixture. Once the panna cotta has cooled, close the jars or cover the ramekins with plastic wrap to prevent them from drying out. Refrigerate for 6 hours or overnight.
- In a large saucepan of cold water, add the lemon slices, bring to a boil and simmer gently for about 10 minutes. Drain.
- In a small saucepan, combine the water, sugar, and lemon juice. Add the lemon slices and bring to a boil. Simmer very gently for about 20 minutes or until slightly syrupy. Let cool.
- Carefully unmould the panna cotta by inverting onto a plate. Top with syrup and a lemon slice.