From the book "L’Armoire à Confitures" by Laurent DUTHEIL and Jane & Glyn Phillips (Sadly now out of print) (Notes in italics are by the friend who sent me the recipe)
Ingredients: 1 kilo of apricots / 750g of sugar
Cut apricots into four pieces. Remove and discard the stones. (Note from me: if the apricots are small – and jam apricots often are – I cut them in half as I like bigger pieces of apricot in my jam).
Mix the fruit and sugar in a stainless steel container and leave to macerate for 18 hours. (Note from me: maybe about 12 hours if the fruit is very ripe and squishy)
Cook on a low heat for about 15 to 20 minutes. Stir from time to time. (Note from me: low heat is important; take care the jam doesn't “catch” at the bottom of the pan).
The jam is cooked when the juice has thickened. (I still do the blob on a cold saucer test to check that it is setting. However, you will probably find that the set is runnier than British jelly set.)
Put into pots. Cover and seal using the “upside-down” method.
Use plain, white, granulated or caster sugar. Recommended ratio of sugar to fruit is between 750g and 800g to 1 kg of fruit – depending on sugar content of fruit.
Minimum recommended is 700g sugar per kilo of fruit. The sugar is added to the fruit and left for some hours in a cool place prior to cooking. A plastic or ceramic container can be used but not aluminium. Ideal temperature is between 12 – 16°C but the fridge is too cold.
Raspberries and other very fragile fruits – 8 hours
Strawberries – 10 hours (add juice of 3 lemons per kilo of fruit after maceration)
Plums – 12 hours
Peaches and apricots – 18 hours
Firm fruits can be stirred to distribute the sugar during maceration but delicate fruits should not be.
The macerating draws the moisture from the fruit, allows faster cooking and this both preserves the flavour of the fruit and saves energy.
Upside-down method of sealing
Sterilise jars in the oven (or whatever is your preferred method of sterilisation). Don’t cool: pour the jam into the warmed pots as quickly as possible. Tighten lids straight away so that the jam produces a vacuum as it cools. Turn the pots upside-down immediately and leave in this position until cold. Then turn upright.