01 - Lightly oil or spray 6 small ramekins or glasses (4–6 oz capacity) to prevent sticking.
02 - Sprinkle gelatin over 2 tbsp cold water in a small bowl. Let stand for 5 minutes until absorbed and softened.
03 - Combine cream, milk, sugar, lemon zest, and salt in a saucepan. Heat over medium until just steaming, stirring occasionally to dissolve sugar. Do not boil.
04 - Remove from heat. Whisk in bloomed gelatin until completely dissolved into the warm cream mixture.
05 - Stir in lemon juice and vanilla extract until fully incorporated and smooth.
06 - Pour through a fine mesh sieve into a measuring jug or pitcher to remove lemon zest pieces and any undissolved gelatin.
07 - Divide mixture evenly among prepared ramekins. Let cool to room temperature, then refrigerate for at least 4 hours or overnight until fully set.
08 - Preheat oven to 400°F for roasting grapes.
09 - Toss 1 cup grapes with olive oil, honey, and thyme if using. Spread on parchment-lined baking sheet in a single layer.
10 - Roast for 10–12 minutes until grapes are softened, juicy, and caramelized. Remove from oven and let cool completely.
11 - Cut remaining 1 cup grapes in half. Keep refrigerated until ready to serve.
12 - Unmold panna cottas onto plates or serve directly in glasses. Spoon roasted grapes and their pan juices on one side, scatter fresh grape halves on the other. Garnish with additional lemon zest or thyme if desired.