Add the pitted and halved apricots, sugar, lemon juice, vanilla extract, and salt to a large heavy-bottomed pot or jam pan. Stir well to combine, breaking down some of the apricots slightly as you mix. This helps the sugar dissolve evenly and start extracting the apricot juices. Place the pot over high heat and bring the mixture to a rolling boil, stirring occasionally to prevent sticking on the bottom.

Once boiling, maintain a vigorous rolling boil and stir frequently for 8-10 minutes. The jam will foam and bubble—this is normal as water evaporates. I like to use a wooden spoon and scrape the bottom of the pot often to prevent scorching, which can give the jam a bitter flavor. Watch for the mixture to thicken noticeably and darken slightly in color, which indicates pectin development and proper gel formation.

Remove the pot from heat and place a drop of jam on a frozen plate (place a small plate in the freezer before starting). Let it cool for 30 seconds, then push the jam gently with your finger—it should wrinkle and hold its shape rather than run back together. If it's still too runny, return to heat for another 1-2 minutes and test again. The jam should reach approximately 105°C (220°F) on a candy thermometer for proper setting.

While the jam is still hot, carefully pour it into sterilized glass jars, leaving about 2 cm (3/4 inch) of headspace at the top. Wipe the rims clean with a damp cloth to remove any jam residue, then place sterilized lids on top and screw the bands on finger-tight. I find that working quickly while the jam is hot helps the lids seal better, so don't delay between cooking and jarring.

Place a rack or folded towel in the bottom of a large pot and fill it with enough water to cover the jars by about 1-2 inches. Gently place the filled jars on the rack, ensuring they don't touch each other. Bring the water to a rolling boil and maintain the boil for 10 minutes to create a proper vacuum seal. This step kills any remaining bacteria and ensures your jam will keep safely for months.

Carefully remove the jars from the boiling water using a jar lifter and place them upright on a clean kitchen towel or wooden surface to cool completely—do not move them for at least 12 hours. As they cool, you'll hear a satisfying 'pop' sound as the lids seal. Once fully cooled, press the center of each lid; it should be slightly concave and not flex. Store the sealed jars in a cool, dark place for up to one year.