This didn't actually come from a foody mag, it came from one of the four 'rubbish mags' (my name for them) that I succumb to each week. Tesco had some raspberries cheap so I grabbed them to have a try. It really was delicious, made half and half with sparkling water and should be wonderful with sparkling white wine. It does need to be chilled for maximum deliciousness.
Basically it's caster sugar (about 300g - ish), two lemons and one orange, all chopped into bits, quite a lot of raspberries (the recipe said 500g, I only had half that and it was still scrummy) and some water (about 300 ml).
Bung it all in a saucepan and slowly bring to a boil. I then let it simmer for a time and used a potato masher to squidge it all down. Then allow to cool before pouring it through a sieve, squeezing down with a spoon or ladle to get all the juices through. Discard the resulting pulp.
It keeps for a week in the fridge and is definitely one I will do again.