Combine. Add diced potatoes into the Instant Pot. Pour in 1 cup of water or broth, and sprinkle with salt.
Prep. Secure the Instant Pot lid and be sure the steam vent is set to "SEALING" (not "venting").
Cook. Press MANUAL/PRESSURE COOKE and set the timer for 9 minutes on HIGH PRESSURE. Allow Instant Pot to come to pressure and cook for 9 minutes (in my test batches, it took 12-15 minutes to come to pressure)
Quick Release Steam. After 9 minutes of cooking, press CANCEL, and carefully switch the vent to "VENTING" to quick release steam from the Instant Pot. (It takes 1-2 minutes for the steam to release fully)
Mash. Carefully open the lid. Add 1/2 cup milk, and 4 Tablespoons butter/ghee/oil to the potatoes. Use a potato masher to mash the potatoes to your desired smoothness, adding more milk and/or butter, as desired. (You can also use a hand mixer on the lowest speed to mash your potatoes, but try not to over-beat, as this can cause red and yellow potatoes to get gluey.)
Taste & Adjust. Taste and add more salt as desired. Garnish with an extra pat of butter or drizzle of olive oil, a little bit of black pepper, fresh herbs, etc.
Serve & Store. Enjoy right away with gravy or an extra pat of butter. Store leftover mashed potatoes in an airtight container in the fridge 2-3 days. Reheat with an extra drizzle of milk or pat of butter, as needed.
TOTAL TIME: These take about 15 minutes to come to pressure + 9 minutes to cook + 5 minutes to release the steam + mash. Once you've prepped the ingredients, you're looking at about 30 minutes start-to-finish.