Cut the peach crosswise and pour boiling water over it, after which it is easy to peel. Remove the peel from the stone and cut into pieces. Carefully rinse the raspberries.
Put the brown sugar with the fruit in a coated pan and let it caramelize over high heat. Simmer for a shorter or slightly longer time, depending on how you want the consistency.
The longer the cooking time, the more the fruit will break down. Serve immediately. The sauce tastes very good with vanilla ice cream.