How to Make It
Preheat the oven to 425°. Stem and wash the grapes well and pat dry. In a medium bowl, toss the grapes with the shallot, olive oil and salt; season with pepper. Spread the grapes on a small rimmed baking sheet and roast for 10 minutes, stirring once. Continue roasting for another 5 to 7 minutes, until most of the grapes have burst and their juices thicken; watch carefully to make sure that the juices do not burn. Scrape the grapes into a bowl and let them cool to room temperature, about 30 minutes.
Reduce the oven temperature to 350°. If the ricotta seems wet, drain it in a sieve lined with paper towels to remove excess moisture. Butter a 2-cup soufflé dish. Fold an 18-inch-long sheet of parchment paper in half lengthwise and trim to a 4-inch width. Wrap the parchment around the inside of the soufflé dish to form a collar that extends 2 inches above the rim; secure the collar by tucking one end into the fold of the other to prevent overflow.
In a medium bowl, mix the drained ricotta with the Parmigiano-Reggiano, egg, chopped thyme and zest until the mixture is combined and smooth; season with salt and pepper. Spread the cheese in the prepared dish. Set the dish on a baking sheet and bake for about 50 minutes, until the center is barely set and the top is nicely browned. Remove the dish from the oven and let it stand for 10 minutes, then remove the parchment collar. Let cool another 30 minutes.
Turn the baked ricotta out onto a small plate, then use a second plate to turn it right side up. Transfer the cheese to a serving plate and top with the grapes. Garnish with thyme and serve warm or at room temperature.
Variation: To garnish the ricotta simply, roast a cluster of grapes in a 500° oven for about 8 minutes.