01 - Lightly oil or spray 6 small ramekins or glasses with 4–6 oz capacity.
02 - Sprinkle gelatin over 2 tbsp cold water in a small bowl. Let bloom 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 - Add lemon juice and vanilla. Whisk until thoroughly combined.
06 - Pour through a fine mesh sieve into a jug to remove zest and any lumps.
07 - Divide evenly among prepared ramekins. Cool to room temperature, then refrigerate at least 4 hours or overnight until set.
08 - Preheat oven to 400°F for roasted grapes.
09 - Toss 1 cup grapes with olive oil, honey, and thyme. Arrange on parchment-lined baking sheet. Roast 10–12 minutes until soft and caramelized. Cool completely.
10 - Halve remaining 1 cup grapes. Keep chilled until serving.
11 - Unmold panna cottas onto plates or serve in glasses. Spoon roasted grapes and juices on one side, scatter fresh grape halves on the other. Garnish with lemon zest or thyme if desired.