Once they’re cooked, measure out how many cherries you have (including the juice.) Use 3/4 of the amount of sugar. For example if you have 4 cups of cooked cherry matter, add 3 cups of sugar. It may seem like a lot, but that amount of sugar is necessary to keep the jam from spoilage.
Stir the sugar and the cherries in the pot and cook over moderate-to-high heat. The best jam is cooked quickly. While it’s cooking, put a small white plate in the freezer. Remain vigilant and stir the fruit often with a heatproof utensil. Scrape the bottom of the pot as you stir as well.
Once the bubbles subside and the jam appears a bit thick and looks like it is beginning to gel, (it will coat the spatula in a clear, thick-ish, jelly-like layer, but not too thick) turn off the heat and put a small amount of jam on the frozen plate and return to the freezer. After a few minutes, when you nudge it if it wrinkles, it’s done.
