Add beans, onion (optional), salt, vegetable broth, and water to the Instant Pot. Pressure cook on high for 30 minutes (it will take about 8 minutes for the Instant Pot to pressurize before cooking begins). Then let the beans rest in the pot for 20 minutes so the steam can dissipate naturally (this means you don't push any buttons — we recommend setting another timer so you’ll remember to remove the lid after 20 minutes).
Carefully remove lid once steam has fully escaped. The beans should be tender and perfectly cooked, but if they're not that's usually caused by having old beans or hard water – you can seal the lid again and pressure cook on high for an additional 10-20 minutes, or until they're tender.
Remove onion and strain off any excess cooking liquid (or sauté for 10 minutes with the lid off, stirring frequently, to evaporate excess liquid).
Enjoy immediately, or store cooled leftovers in the refrigerator up to 5 days or in the freezer up to 1 month.
Video
Notes
*Nutrition information is a rough estimate calculated with store-bought vegetable broth.