Combine rosehips and water in a pot. Bring to a boil, then simmer until very soft, about 25 minutes.

Blend the mixture until smooth, then strain through a fine sieve to remove the tiny hairs and seeds.

Return the strained liquid to the pot, stir in sugar, and bring back to a simmer.

Whisk in the cornstarch slurry and cook 2 minutes until slightly thickened.

Serve warm or chilled, topped with toasted almonds and a spoonful of whipped cream.