01 - Lightly oil or spray 6 small ramekins or glasses (4–6 oz capacity).
02 - Sprinkle gelatin over 2 tbsp cold water in a small bowl. Let stand for 5 minutes until absorbed.
03 - Combine cream, milk, sugar, lemon zest, and salt in a saucepan. Heat over medium until steaming, stirring to dissolve sugar. Do not boil.
04 - Remove from heat. Stir in bloomed gelatin until completely dissolved.
05 - Whisk in lemon juice and vanilla extract until smooth.
06 - Strain mixture through a fine mesh sieve into a jug. Divide evenly among prepared ramekins.
07 - Cool to room temperature, then refrigerate at least 4 hours or overnight until set.
08 - Preheat oven to 400°F. Toss 1 cup grapes with olive oil, honey, and thyme. Spread on parchment-lined baking sheet and roast 10–12 minutes until soft and caramelized. Cool completely.
09 - Halve remaining 1 cup grapes and keep chilled.
10 - Unmold panna cottas onto plates or serve in glasses. Arrange roasted grapes and their juices on one side, fresh grape halves on the other. Garnish with additional lemon zest or thyme if desired.