In a large saucepan, mash the raspberries with a potato masher. Add the sugar and lemon juice, and stir to combine. Cut the vanilla bean in half. Split open each half and scrape the seeds into the jam mixture. Throw the pods in the pot as well.
Over medium heat, cook the mixture, stirring gently, until the sugar is dissolved. Add ¼ teaspoon fresh ground pepper (more or less, to taste).
Raise the heat to medium-high and boil gently, stirring frequently, until it begins to thicken to a jam-like consistency. This will take approximately 10–20 minutes, depending on the intensity of the heat.
One way to test if the jam is ready is to put a small spoon in your freezer when you start the recipe. When you see the jam is thickening, turn off the heat. Take the cold spoon out of the freezer, scoop up a small amount of the jam, and return the spoon to the freezer (on a small plate, to avoid a mess). After 2–3 minutes, take the spoon out of the freezer and hold it up sideways. If it has the consistency of jam out of the refrigerator, it’s ready. If the jam drips off the spoon like thin soup, continue heating the jam on the stovetop over medium heat until you reach the desired consistency. Remember: It will thicken when you refrigerate it, so don’t overcook it.
Remove the vanilla bean pods from the saucepan and discard. Ladle the jam into a jar or bowl, and allow to cool completely at room temperature before refrigerating. Jam will last 2–3 weeks in the refrigerator.
Suzanne Krowiak is a Master Food Preserver and founder of Indy Food Swappers. A former television writer and producer, she currently teaches classes and gives presentations on food preservation and other D.I.Y. food topics. Follow her @indyfoodswap on Twitter.