Put trivet inside pressure cooker with your frozen roast on top.
Pour broth over the top, sprinkle in onions and put any and all seasonings you like on top of your meat.
Close lid and steam valve and set to high pressure for 90 minutes followed by a natural release.
If the weight of your roast differs, adjust by 10 minutes per pound.- 2 lbs = 80 minutes- 4 lbs = 100 minutes
Remove meat and allow to rest if slicing, or remove trivet and shred right in pot with liquid. If you want to thicken liquid, remove meat, set to saute and in a small bowl whisk a few tbsp of cornstarch with some of your hot liquid. Pour that in, stir and allow to thicken, pour this on top when serving.