Many traditional recipes use an equal amount of sugar to fruit, by weight, but I find it’s okay to decrease it to these proportions. Sugar is both a thickener and a preservation agent. If you reduce it too much more, your jam may not thicken and won’t keep for a long time. (Which is okay if you want thinner jam, you keep it in the refrigerator, and eat it relatively quickly.) This recipe can be scaled up or down, depending on how many strawberries you have. But if you want to make a lot more, best to make it in a couple of batches. To prepare the jars, pour boiling water into them, as well as into the lids. Let them sit 5-10 minutes, then carefully pour out the hot water and set them upside down on a cooling rack until ready to fill.