Fill a medium-sized pot halfway with water and bring it to a boil over high heat.
Peel the plantains and cut them into 3–4 chunks each. (Tip: If the plantains are cold, let them sit at room temperature for 20–30 minutes to make peeling easier.)
Once the water is boiling, add plantains and salt.
Reduce the heat to medium-low and simmer for 20–25 minutes, or until the plantains are fork-tender. To check for doneness, insert a fork or toothpick—if it goes in easily, they’re ready.
Once tender, drain the plantains and transfer them to a large mixing bowl.
Add the salted butter to the bowl and mash the plantains and butter with a fork or potato masher until smooth and creamy.
Add cold water and a few ice cubes while mashing to make the Mangú extra smooth and creamy—trust me, it works! Give it a taste and add more salt or butter if needed to suit your preferences.
Serve the mangu hot with your favorite toppings, such as sautéed pickled onions, fried cheese, fried eggs, crispy fried Dominican salami, or avocado slices.