Place prepared potatoes in a steamer basket. Alternatively, place them straight in the pot (see notes).
Pour water or broth into the pot.
Lock the lid, set the knob to SEALING, then cook on manual high pressure for 7 minutes (Add additional time for larger potato cubes, about 2-5 minutes)
Perform a quick release (QR) to release all the steam and pressure.
Open the lid and check the potatoes with a knife. If there is any resistance, the potatoes are not cooked all the way. Add 1 more cup of water, replace the lid, and cook for an additional 2 minutes.
Drain the water out of the Instant Pot. If you placed the potatoes straight into the pot (no steamer basket), you should not have any additional liquid in the pot, but if you do, drain it.
Add butter, half and half, and salt/pepper. Mash to your desired consistency using a potato masher. The potatoes may be kept on "keep warm" in the Instant Pot until ready to serve.