Place the trivet into the basin of the instant pot. To the chicken bouillon or 1 cup of water, add 1 teaspoon of salt.
Peel the potatoes and divide them into quarters (approximately 1 inch in thickness, large enough to prevent them from collapsing under the trivet). Proceed to arrange the potatoes on the trivet in a manner that prevents the largest fragments from penetrating.
Cover with a lid, adjust the valve to the "sealing" position, and cook for 10 minutes under manual high pressure with a rapid release. Once the pressure has been released, remove the trivet using tongs or an oven mitt, followed by the lid. Avoid emptying the water.
Warm milk should be added to the mashed potatoes after mashing them to the desired consistency. Then, incorporate the softened butter just until combined. Blend the potatoes with an electric hand mixer until no particles remain for a more uniform consistency. If preferred, season to taste with additional salt.