Prepare a small boiling water bath canner and 4 half pint jars.

Chop or crush the plums, remove the pits, and combine them with the sugar and vanilla bean seeds. Stir to incorporate the sugar.

Once the sugar is dissolved, set the pan on the stove over high heat and bring to a boil.

Cook, stirring regularly for 15 to 25 minutes, until the fruit thickens and reduces by at least one-third.

Taste and add lemon juice as needed.

When the jam seems quite thick and glossy, remove it from the heat.

Funnel the jam into the prepared jars. Wipe the rims, apply the lids and rings, and process in a boiling water bath canner for 10 minutes.

When time is up, remove jars from the canner and set them on a folded kitchen towel to cool.

When jars are cool enough to handle, test seals. Sealed jars are shelf stable for at least one year. Any unsealed jars should be refrigerated and used promptly.