Wash the potatoes, peel them (optional) and cut into quarters.
Add water, potatoes and salt to the instant pot.
Secure the instant pot lid and close the pressure release valve. Select manual/High pressure and cook at high pressure for 10 minutes.
When the timer beeps, allow the pressure to naturally release for 3-5 minutes, and then quick release the remaining pressure.
Carefully open the lid. Add the milk, sour cream, butter, bouillon paste, and salt and pepper.
Mash everything combine, but be careful not to over mash the potatoes, which leads to gummy mashed potatoes instead of fluffy mashed potatoes.
Taste and add more seasonings, as needed.
Make Ahead Tip:Mashed potatoes can stay in the instant pot on "keep warm" for 1-2 hours. Gently stir them and taste them before serving. They may need another splash of milk and a little salt or additional seasonings.*You can double or triple this recipe for a 6 or 8 quart instant pot. The water amount and cooking time will stay the same. Just be sure you don't go above the "fill" line".