01 - Lightly oil or spray 6 small ramekins or glasses with 4-6 oz capacity.
02 - Sprinkle gelatin over 2 tablespoons 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 heat 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 - Pour through a fine mesh sieve into a pitcher to remove zest and any lumps.
07 - Divide evenly among prepared ramekins. Cool to room temperature, then refrigerate for 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 refrigerate until serving.
10 - Unmold panna cottas onto plates or serve in glasses. Arrange roasted grapes and juices on one side, fresh grape halves on the other. Garnish with lemon zest or thyme if desired.