Prep the rhubarb: Rinse the stalks well. Trim off leaves (they’re not edible) and any rough ends. Chop the stalks into small, even pieces, about ½ inch thick.

Mac­erate with sugar: In a large saucepan, combine chopped rhubarb and 1 cup sugar. Add the zest of half the lemon and the juice of the whole lemon. Stir, then let it sit 15–20 minutes until some juices release.

Start cooking: Set the pan over medium heat. If the pot looks dry, add 2 tablespoons water to prevent sticking. Cook, stirring often, until the rhubarb softens and begins to break down, about 10 minutes.

Add flavor: Stir in vanilla and a pinch of salt. Taste carefully. If you want it sweeter, add the remaining sugar a couple of tablespoons at a time, stirring until dissolved.

Simmer to thicken: Reduce heat to medium-low. Continue to cook, stirring frequently to prevent scorching, until the mixture is glossy and thick, 15–25 minutes. It should mound softly on a spoon.

Check doneness: Place a small plate in the freezer for 5 minutes. Dab a little jam on the cold plate, wait 30 seconds, then push it with your finger. If it wrinkles slightly and doesn’t run, it’s ready. If not, simmer 5 more minutes and test again.

Cool and jar: Remove from heat and let it rest 5 minutes to settle. Transfer to clean glass jars. For everyday use, simple clean jars are fine since this is a fridge jam.

Label and chill: Let cool to room temperature, then cover, label with the date, and refrigerate.