Place the brie onto a board lined with baking paper. Cut 4-5 small bunches from the grapes and place in a bowl. Remove the remaining grapes from the stems, cut some in half and place in the bowl with the bunches.
Pour the honey into a medium non-stick frying pan. Add the balsamic vinegar, thyme and chilli flake. Bring to the boil, stirring over medium heat. Add all the grapes, boil gently for 3 minutes.
Use a slotted spoon to remove the grapes to a bowl. Leave the syrup in the pan and remove from the heat. Cool the grapes for 30 minutes.
Spoon the cooled grapes over the cheese, placing any extra in a serving bowl. Sprinkle the pistachios over the grapes. Return the syrup to the heat and bring to the boil. Boil for 2-3 minutes until thickened slightly. Cool for 2 minutes then spoon over the cheese. Serve with crostata or as part of a charcutier board.