Or Rumtopf if you want the German, they are behind this idea, and a very good idea it is too!
Take 440g (about 1lb) or strawberries and mix with 220g (about 1/2lb) of sugar. Leave for 30mins or so.
Put the sugared strawberries plus all the juice and sugar into a rumtopf jar. You don't have to have a special jar, but we found this one in a charity shop any large, lidded jar will do.
Pour rum on top of the berries until they are completely covered, we used about 750ml. Put the lid on and sit the jar safely on a shelf.
As more fruit comes into season (raspberries, cherries, blackberries, blackcurrants, red currants etc) repeat the process of fruit, half the weight of sugar, add to the jar and cover with rum. Frozen fruit and tinned fruit can be used too, a few pineapple slices are good.
The jar should be full by the end of the summer, leave it for a few months for all the flavours to mix and just before Christmas strain the liqud off for drinking. The fruit can be eaten too if you like.