First mix the frozen raspberries with the sugar and cover it well with plastic wrap. Now heat it up on a bain marie for around 3 hours on a low heat. Then remove the wrap and let the liquid drain on a sieve that’s lined with a kitchen paper. Do this for at least 3 hours in your fridge.
Pour the raspberry broth into a saucepan and mix it with the agar powder. Then bring this to a boil for at least 1 minute. Once it has boiled pour it into a bowl and let it cool down completely in your fridge. Then transfer it into a blender and blend it into a smooth gel.