Prepare the fruit: Place the halved, pitted apricots in a large, heavy-bottomed pot along with the lemon juice. Stir gently to combine.

Macerate (optional but recommended): Cover the pot and let the apricots sit at room temperature for 3 to 4 hours, or overnight in the refrigerator. This draws out the juices.

Cook to boiling: Place the pot over medium-high heat and bring the mixture to a full, rolling boil, stirring frequently to prevent scorching. Cook for about 10 minutes until the fruit softens significantly.

Add sugar and pectin: Thoroughly mix the granulated sugar and pectin (if using) in a small bowl before adding it to the boiling fruit mixture. Stir constantly until the sugar is completely dissolved.

Boil rapidly to setting point: Increase the heat and continue to boil rapidly, stirring often, until the jam reaches the setting point (220°F or 104°C on a candy thermometer), or when a small dollop wrinkles when chilled.

Skim and jar: Remove the pot from the heat. Skim off any pink foam that has risen to the surface using a slotted spoon. Ladle the hot jam into sterilized jars, leaving 1/4 inch headspace. Wipe rims clean and seal with lids.