Place the pumpkin juice in a saucepan, bring to the boil and reduce by half. In a separate saucepan, heat the butter until it turns golden brown. Whisk the melted butter into the reduced pumpkin juice. Add the sherry vinegar, season to taste and pour into a squeeze bottle.
Bring a saucepan of salted water to a rolling boil. Pick the leaves from the rosemary and blanch for 20 seconds. Dr