Preheat oven to 220˚C.
Place the grapes onto a baking tray (line with baking paper if you prefer), scatter with the thyme leaves and drizzle with the vinegar and 1 tablespoon of olive oil. Toss briefly to coat. Roast them until they are starting to collapse, 10-12 minutes.
Remove the tray from the oven and gently flip the grapes over. Add the block of feta, drizzle the feta with a little olive oil and season with sea salt and black pepper. Return to the oven until the feta is soft and the grapes are starting to burst, about 10 minutes.
The just-baked grapes will be hot, so allow to cool slightly before serving warm with crusty bread or crackers.
