Heat the rose water in a small saucepan over medium heat to 60°C (140°F). Add the rose petals, remove from the heat and refrigerate for 1 hour to infuse.
Place the rose water and the petals in a vita-prep (or high-speed blender) and purée until smooth. Strain the mixture through a chinois to remove the rose pieces. Place in a small saucepan over high heat. Bring to the boil. Add the aga