Prepare the potatoes: Peel the potatoes and roughly cut them into approximately 1-inch cubes.
Add to the Instant Pot: Place the potato cubes in the stainless steel inner pot of the Instant Pot. Pour water over them until they are completely covered (approximately 4 to 4½ cups).
Cook: Place the lid on the Instant Pot and lock it by turning it clockwise until it chimes. Ensure the Pressure Release knob is set to Sealing. Select the Pressure Cook option on High for 4 minutes and press Start.
Release the pressure: When the Instant Pot beeps at the end of the timer, carefully switch the Pressure Release knob from Sealing to Venting to release the pressure (I recommend using a wooden spoon or something similar to protect your hand from any escaping water or steam). Turn the lid counterclockwise to open the pot once the stainless steel float valve has dropped.
Drain: Using a towel or potholders, carefully lift the inner pot and dump the potato-and-water mixture into a colander over the sink. Let the potatoes drain in the colander for a few minutes.
Mash: Return the drained potatoes to the inner pot. Using a potato masher, mash until the potatoes are smooth.
For basic mashed sweet potatoes: If you prefer your sweet potatoes plain and simple, without the miso-maple flavor, stop here. Taste and, if desired, add ¼ teaspoon fine sea salt before serving.
For miso-maple mashed sweet potatoes: Add ¼ teaspoon of garlic powder, miso paste, maple syrup, and unsweetened plant milk. Stir the potatoes well to fully incorporate these ingredients, taking special care to make sure the miso paste is broken up and thoroughly blended in. Taste. If you want a more pronounced garlic flavor, add an additional ¼ teaspoon garlic powder. Serve warm.