Prepare the fruit: If using fresh cherries, pit and halve them. If using frozen, run under cool water briefly to separate them, keeping them mostly frozen.

Combine the cherries, sugar, and lemon juice in a large, heavy-bottomed pot or Dutch oven. Stir well and let it sit for about 10 minutes to start drawing out the juices.

Bring the mixture to a rolling boil over high heat, stirring constantly to prevent scorching. Once boiling, quickly whisk in the pectin until fully dissolved, about 1 minute.

Continue boiling vigorously, stirring often, for 10 to 15 minutes, or until the jam reaches setting point (approximately 220°F or 104°C on a candy thermometer). The mixture should thicken noticeably.

Remove the pot from the heat. Gently stir in the vanilla bean paste until incorporated. Allow the jam to cool slightly for about 5 minutes before jarring to ensure even distribution of the vanilla.

Ladle the hot jam into sterilized jars, leaving 1/4 inch headspace. Wipe rims clean, affix lids and bands. Process in a boiling water bath for 10 minutes for shelf stability, or refrigerate immediately for short-term storage.