Wash and clean strawberries very well, removing the stems. Chop smaller berries into fourths, and larger berries into eighths.
Wash 2 small glass jars and their lids. Keep the jars in a warm place, or in an oven heated to 200°F. By warming the jars, you prevent them from breaking when pouring in the hot jam. It is very important you do not skip this step if you plan to can the jam.
In a large pan over medium heat, combine the chopped strawberries with sugar. With a knife, split the vanilla bean lengthwise and scrape out the seeds. Add both the seeds and the bean to the strawberry mixture. Whisk occasionally until it starts simmering, then lower the heat slightly and let it simmer for 40-60 minutes. Stir occasionally so the jam doesn't burn on the bottom of the pan.
After 40-60 minutes, test the jam by dropping a bit of juice from the pan on a plate. If it doesn't spill around when the plate is moved, the jam is ready.
Once the jam is ready, add a pinch of citric acid. Stir and remove the pan from the heat.
Fill the warmed jars with the hot jam almost to the top, then immediately close them tightly with the lids. Place them on the kitchen counter upside-down. This ensures the lids are perfectly sealed. Let the jars remain upside-down until they cool to room temperature.
Keep the sealed jars in a dry place at room temperature for up to a year. After opening the jar, keep it in a cool place.