You'll need 4 1/2 pounds fresh, not overly ripe but blemish-free blackberries, and 4 1/2 pounds powdered sugar (the kind that does not contain starch, and feel free to adjust quantities if need be). Place everything in a pot, taking care not to crush the fruit, and set it over the fire. The heat will make the berry skins split and their juices will run clear without the least hint of cloudiness (which you would have seen had you crushed them). Once the sugar has dissolved, cook just a few minutes longer as the syrup will be ready quickly.

Strain the syrup through an extremely fine strainer, without pressing the fruit that gets caught, and you won't have to clarify it.

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