If you've never preserved anything before, start here. This is the simplest, least stressful jam recipe imaginable. There's no standing at the hob, no boiling, and no checking for setting point. The result is a decadently soft-set jam, but it must be stored in the fridge.
I made a scant 750g jar of this yesterday evening whilst the oven was on and cooking dinner: efficiency in several forms, then. My grandmother and I did discuss the suitability of other fruits for making this. We decided that the very soft nature and high sugar content of raspberries (or fruits related to them, for example loganberries) was the key factor, and therefore it was a raspberry-restricted recipe.
If you hadn't guessed, this is another recipe brought to you by my father's allotment of bountiful wonders. It used all the raspberries that had been picked yesterday.
Method
Preheat your oven to 200° Celsius.
Spread your raspberries evenly across one large, high-sided oven dish and place your sugar in another suitable oven-proof container. I used a flan dish for the raspberries and a casserole for the sugar.
Place both dishes in the oven for 20 minutes, or until the fruit is beginning to bubble and the sugar is hot. (It won't have melted.)
When the fruit and sugar have reached temperature, remove the dishes from the oven and tip the fruit into the sugar and mix well. Also mix very carefully: you have heaps of very hot sugar splashing about. The potential for burns and scalds is high.
When the sugar has dissolved, pour the jam into sterilised jars1 (in this instance, one 750g jar), allow to cool, and then refrigerate.
1 Sterilise jars by washing in hot, soapy water and placing in a slow oven for 20 minutes.
Music to cook to: Dream of Me, by Kristina Train