Add the raspberries, sugar, and lemon juice to a jam pan or any wide non-reactive pot. Slit the vanilla bean (if using) lengthwise and scrape the seeds from it with a small knife and add to the jam pan. Stir carefully with a wooden spoon, cover with a towel, and let macerate for 2 hours at room temperature.
Bring the mixture to a boil over medium-high to high heat, depending on how hot your burner gets, stirring frequently, and cook for about 20-25 minutes, until a drop of the jam on a cold plate forms a thick mound and runs off slowly.
Ladle the jam into four sterilized half-pint mason jars, add lids and rings, tighten finger-tight, and process them in a boiling-water bath for 10 minutes.
Let the jars cool overnight or up to 24 hours, remove the rings, and check the seal on each jar. Store in a cool, dry, and dark place for up to a year for optimum freshness. The jam will begin to lose its taste quality after a year slowly but will be safe to consume well after that. Store open jars in a refrigerator for up to 3 weeks.
Alternatively, ladle the jam into clean half-pint jars, cover them with tight lids, chill at room temperature, and refrigerate for up to 3 weeks.