Place a small saucer in the freezer—this will be your setting test throughout the cooking process. Prepare your canning jars and lids by rinsing them thoroughly with boiling water and setting them aside to dry; this sterilizes them and keeps them warm for filling. Trim your rhubarb and cut it into 1/2-inch pieces, and measure out all your ingredients so everything is ready when you begin cooking.

Combine the rhubarb pieces and lemon juice in a large, heavy-bottomed pot (at least 8-quart capacity to prevent boiling over). Bring to a boil over medium-high heat, stirring occasionally to help the rhubarb break down. Let it boil for 10 minutes—the rhubarb will soften and release its juices, creating the foundation of your jam's flavor.

Stir the pectin into the boiling rhubarb mixture, breaking up any lumps to distribute it evenly throughout the fruit. This will activate the pectin and help your jam set properly. Continue boiling for another 10 minutes at a rolling boil, stirring frequently to ensure the pectin is fully incorporated and working throughout the mixture.

Add the sugar and pinch of salt to the pot, stirring constantly until the sugar dissolves completely—this usually takes 2-3 minutes. I like to add the salt at this stage because it balances the tartness of the rhubarb and enhances the overall flavor without making it taste salty. Return to a rolling boil and cook for 15-20 minutes, stirring frequently to prevent sticking on the bottom of the pot. Start testing for doneness after 15 minutes by dropping a small spoonful of jam onto your frozen saucer, letting it cool for a minute, then pushing it with your finger—it's ready when it wrinkles and doesn't run back together.

Once the jam reaches setting point, carefully ladle it into your prepared warm jars, leaving about 1/4-inch headspace at the top. Immediately place the lids on the jars and screw the bands on finger-tight. I prefer to let the jars sit at room temperature for 24 hours undisturbed—this allows them to seal properly and the jam to fully set before you move or store them.