This is a simple yet wonderful sauce.
Just get some stock syrup which is
125g water and 125g sugar, boil it together until desolved.
then for the raspberry (You can also use any other berries)
Place 1kg of raspberry into the stock syrup and boil and mash to get the full flavor, after cooking run through a sieve to get the juice only, the remainder can be eaten by yourself or thrown away.
Wasn't that easy.