Rinse the wild blueberries and sort through them, removing any stems, leaves, or berries that have gone soft or shriveled. Frozen wild berries go into the pot straight from the bag without thawing.

Add the blueberries, lemon juice, and sugar to a wide, heavy-bottomed pot all at once. There's no need to macerate the fruit first or hold the sugar back.

Bring the mixture to a boil over high heat, stirring constantly and mashing the berries lightly against the side of the pot as they soften so they release their juices and the sugar dissolves.

Keep the jam at a hard boil, stirring the whole time, until it reaches the gel stage at 220 degrees F on an instant-read thermometer. Expect this to take 12 to 15 minutes once the jam has come to a full boil. If you'd rather not use a thermometer, drop a spoonful onto a frozen plate, return it to the freezer for a minute, and push the edge with a fingertip. If it wrinkles and holds its shape, it's done.

Ladle the hot jam into the prepared jars, leaving 1/4 inch headspace. Slide a bubble tool around the inside of each jar to release trapped air, wipe the rims clean, center the lids, and apply the rings to fingertip tight.

Lower the jars into the boiling water bath canner, making sure they're covered by at least 1 inch of water, and process for 10 minutes, adjusting for altitude (see notes). Turn off the heat and let the jars stand in the canner for 5 minutes before removing them.

Cool the jars undisturbed on a towel-lined counter for 12 to 24 hours, then remove the rings and check the seals before labeling and storing.