Bring bay leaf, vinegar, salt, sugar, and 1 cup water to a simmer in a small saucepan, stirring to dissolve salt and sugar.
Add seeds to pickling liquid and bring to a boil. Reduce heat and simmer until tender (they should yield easily between your front teeth), 30–45 minutes. Let seeds cool in liquid; transfer to an airtight container, cover, and chill.
Store pickled seeds in their liquid in the refrigerator up to 3 months.