Panna cotta with rhubarb topping (George Calombaris)

Panna cotta

• oil, to grease
• 410 g pouring (whipping) cream
• 160 g full cream milk
• 50 g sugar
• ¼ tsp mastic gum (see Tips)
• 350 g chilled water
• 3 titanium strength gelatine leaves

Rhubarb topping

• 6 stalks rhubarb (approx. 500 g), trimmed and cut into pieces (7 cm)
• 70 g caster sugar
• 70 g honey
• 70 g water