Wash and peel potatoes. Cut into slices or small cubes and add to a large pot. Fill the pot with enough cold water to cover the potatoes. Add 1 teaspoon of salt. Cover with a lid and bring to a boil. Then remove the lid, reduce heat, and simmer for 15-20 minutes, or until the potatoes are tender. Do not start timing the potatoes until they come to a boil.
While the potatoes cook, heat 6 tablespoons of butter and 3/4 cup of canned milk until warm and the butter is melted. Set aside.
Drain and place potatoes in a mixing bowl.
Add the pepper, the other teaspoon of salt, and the heated milk/butter mixture to the potatoes. Beat with a mixer until creamy, leaving some potato lumps. Heat and add more milk if necessary. The potatoes should be creamy and not dry. Do not overbeat.
Add more salt if needed. Place potatoes in a serving bowl and then add the last tablespoon of butter to the top of the potatoes and let melt. Refrigerate leftovers.
Notes
Stovetop Reheating
To reheat leftover mashed potatoes, place them into a pan. Add 3 or 4 tablespoons of milk (canned or whole milk). Stir. Heat the potatoes until hot. Add additional milk if necessary, so the potatoes are creamy and not stiff.
Microwave Reheating
You can also reheat mashed potatoes in the microwave. Place the leftover potatoes in a microwave-safe bowl. Add 3-4 tablespoons of milk. Stir until creamy, adding more milk if necessary. Heat in 30-second intervals, stirring between intervals, until hot.
Make Your Own Evaporated Milk
If you don't have evaporated milk, you can make your own by adding 3 cups of whole milk to a thick-bottomed saucepan. Bring the milk to a simmer and cook it until it reduces to 1 1/2 cups.