Put all the ingredients into a pot (starting with 2/3 cups of sugar), stir to distribute the ingredients, and put the pot, uncovered on medium low heat until all the sugar melts and the mixture just starts to bubble. (Usually takes just under 10 minutes for me.)

Turn the heat down to low and simmer, uncovered, for 35 to 45 minutes, stirring occasionally. If you can scrape fruit solids off the cooking surface of the pot, your heat's too high. It's better to err on the side of lower heat and longer cook time than to cook the fruit to the point that it begins to stick to the bottom of the pot. Just a little of that mild burn can alter the whole batch in a way you might not like so much.

About halfway through the simmer, take a potato masher or a fork and mash the berries to release some more of their natural pectin and to get the jam to the consistency you like. If you like more whole fruit, less mashing, but give it a few good mashes just to aid the natural thickening.

Check the sweetness 10 minutes before the jam is done to adjust and add more sugar if needed.

Because I like my jam texture something like a thick compote (it's more versatile that way - I can eat it over ice cream, or with yogurt), I don't add pectin or gelatin, and I stop the cooking when the jam has the texture of a thick stew. When it cools, it'll thicken even more, but it won't have that solid gel texture of a storebought jam.

Then just put your jam in a clean and well-dried tight lidded container (doesn't have to be glass), cool completely uncovered, then cover and refrigerate. It'll keep fine for at least a good 6 to 8 weeks.