Place the Mixed red berries in a medium saucepan with just enough Water to cover the bottom and add Granulated sugar to taste; bring to a gentle simmer over medium heat.
Cook, stirring occasionally, until the berries have broken down and released their juices (about 10–15 minutes); mash lightly with a spoon or potato masher for a smoother texture.
If you prefer a seed-free pudding, press the cooked mixture through a fine sieve into a clean pot or bowl, discarding the solids, otherwise leave as is.
In a small bowl, whisk the Potato starch with a little cold water to make a smooth slurry, then slowly stir the slurry into the simmering berry mixture and continue to cook for 1–2 minutes until it thickens and becomes glossy. Stir constantly to prevent lumps.
Remove from the heat and let the pudding cool to room temperature, then transfer to the fridge to chill and set for at least 1–2 hours.
To serve, spoon the chilled pudding into bowls and drizzle with cold Heavy cream; enjoy immediately. Taste the pudding before chilling and adjust sweetness if needed.
