Put the grapes in a bowl and press down on them with your hands, then crush the grapes one at a time between your fingers to break the skin. Use the back of a spoon to press all the grapes through a sieve to obtain as much juice as possible.
In a bowl, incorporate the flour into the juice. Start with a little juice and stir with a whisk, being careful to avoid forming lumps. Add the rest of the juice, mixing constantly for a few minutes until all the lumps have disappeared.
Put the mixture in a pan and heat to boiling, stirring constantly. Boil for 2 minutes and pour the warm mixture into individual molds or dessert dishes. Refrigerate and let rest for at least a few hours. Serve this dessert with a glass of Muscat wine.