Pick over the raspberries carefully, discarding any leaves and stalks along with any mouldy or otherwise suspect fruit. Put half the fruit in a large basin and roughly crush the berries by hand, squeezing them with your fingers. Place them in a heavy stainless steel or copper pan that is large enough to be not more than half full when all the ingredients are added. Add the remaining fruit, whole, and the sugar.

Stir over a low heat for a few minutes to dissolve the sugar, then turn up the heat and bring to the boil. Boil hard for exactly 5 minutes. The jam can be taken off the heat and potted up at this point, and you will have a loose jam with an excellent, fresh flavour. If you want a more traditional, set texture, boil the jam for 7 minutes in total, then test it for setting point: using a teaspoon, let a few drops of jam fall on to a chilled plate. Leave for a moment to cool, then push the jam sideways with your finger. It should crinkle slightly and, when taken between thumb and forefinger, it should be nicely tacky. As soon as it has reached this stage, remove from the pan from the heat.

Pot up the jam in warm, sterilised jars straight away (to sterilise jam jars, just put them through a cycle of the dishwasher, or you can wash them in hot soapy water and then dry in a very low oven). Cover each jar with a wax disc while the jam is still hot, then with a cellophane cover or screw-top.