In the Instant Pot, combine the 40 oz (1134g) of peeled and cubed potatoes, 3 cloves (0. 5 oz / 14g) of garlic, 1 sprig (0. 1 oz / 3g) of fresh rosemary, and 1 cup (8 fl oz / 240g) of chicken broth.
Stir the ingredients thoroughly. Securely close and lock the lid. Select the MANUAL setting and cook at HIGH pressure for exactly 15 minutes.
Once the cooking timer completes, immediately perform a Quick Release to vent the steam. Carefully unlock and remove the lid.
Drain any remaining liquid from the pot.
Using a potato masher or electric beater, begin mashing the potatoes while slowly blending in the 0. 25 cups (2 fl oz / 60g) of milk and 2 tbsp. (1 oz / 28g) of butter until the texture becomes flawlessly smooth and creamy.
Season the mixture with 1 tsp. (0. 2 oz / 6g) of salt, or adjust to your personal taste preference.
Serve warm immediately alongside your favorite main course.
Warm Your Dairy: Before blending, gently warm your milk and butter.
Adding cold dairy drops the temperature of the hot potatoes, forcing you to mix longer. Overmixing activates starches and leads to a gummy, glue-like texture.
Do Not Overwork the Mash: Whether you are using a potato masher or an electric beater, stop mixing the second your potatoes reach a smooth consistency. Overworking is the number one cause of a dense, pasty side dish.