Boil the Potatoes: Add cubed potatoes, water and 1 ½ teaspoon salt to your Instant Pot. Pressure cook in HI pressure for 10 minutes. Quick release the pressure once done.
Heat the Milk: While the potatoes are cooking, in a saucepan over medium-low heat, warm the milk. If you are going to add butter, melt it with the milk. If you are going to add any herb add-ins, steep it with this milk as it warms.
Drain and Dry: Once the potatoes are done, drain and return the Instant Pot. Put on LO saute mode, and let the residual water evaporate completely, so the potatoes are completely dry.
Mash the Potatoes: Using a potato masher (or potato ricer if you prefer) mash the potatoes until smooth. Add the milk mixture little by little, and fold in using a spoon or rubber spatula.