Make the syrup first: combine 300 g sugar, 400 ml water, 4 crushed green cardamom pods and 1 tsp lemon juice in a wide saucepan. Bring to a boil over medium heat, stirring only until the sugar dissolves, then simmer 5 minutes until very slightly sticky. Turn off the heat, stir in 1 tsp rose water and leave the syrup warm.