{Rookie} Backyard Plum Jam

This is what I do (and I'm a rookie, folks):
Adapted from here

For every 2kg of plums, I add approximately...
1 cup water
1.5kg white sugar
a squirt of lemon juice
(That's it!  No pectin, no nothin'!)

Method:

1. Boil the plums in a very large pot, whole, until their skins come off, the water is purple, and the the flesh is soft and taking on the same purple colour.
2. (Meanwhile, you could be washing about 8 jars in hot soapy water, and setting up their lids to boil alongside your plums.  You probably will only need 6 or 7 medium-sized jars, but better to have extra.)
3. Pour off the water (and reserve it for smoothies and other creations) but reserve the cup of water needed for every 2kg of plums.  (Both of these I estimate.)
4. Empty the boiled plums into some other large container (or containers), and place a colander or steamer (I use a steamer because it has a flat base) over the large pot you used for boiling the plums.  Slowly feed the boiled plums into the holey device of your choice, mashing the plums pulp through with a potato masher.
5. Discard the stones (and any skin chunks). 
6. Add plum water, set aside earlier, along with a squirt of lemon juice.
7. (Now you could place the washed jars into your cold oven, spacing them so they do not touch.  Turn the oven on to 160 degrees C.)
8. Return pulp to the stove and boil for 5-10 minutes.  (When the oven reaches temperature, turn it off, and leave the jars waiting in the warm oven for filling.)
9. Pour the the 1.5kg bag of sugar into a large glass bowl and microwave for 4-5 minutes on high (it should be warm to the touch...and careful, the bowl will be hot!).
10. Add the sugar to the hot pulp, stirring until well dissolved.  
11. Put a small plate in your freezer.
12. Heat on med-high (boiling) for 20 minutes, (stirring often), or until the jam reaches setting point -- test by dropping some jam onto the plate from the freezer and tipping the plate.  If it gives a little, like jelly, but doesn't run, you're done!  If it trickles across the plate, lick it clean (muaha!) put the plate back in the freezer and cook for 5 more minutes before performing the same test. 
13. Pour ladels-full through a funnel into your jars (warm from the oven) and close up, label, and finish off as you will.

 NB:  Each time I've made it so far, I've boiled the plums whole the night before and then left them to cool down enough that I can put them in the fridge overnight.  The next day I strain the cool plums out for the mashing and straining, check enough purple water has gone through, and then heat the pulp up to start jam-making (i.e. adding warm sugar and boiling, boiling and boiling).