How to do the perfect mashed potatoes ?

Ingredients

-2 lb. Idaho potatoes
-3 tbsp. Kosher salt
-1 c. milk
-4 tbsp. cold unsalted butter
-½ tsp. fresh-ground black pepper

Directions

Cook the potatoes: 

Heat oven to 250 degrees F. Place the potatoes in a pot and fill with enough water to cover. Add the salt and bring to a boil over high heat.

Reduce the heat to medium and simmer until potatoes are tender -- 12 to 15 minutes. Drain the potatoes, transfer to a baking pan, and place in the oven until thoroughly dried out -- 7 to 8 minutes. (Shake the pan occasionally to ensure all excess water evaporates.)

Puree the potatoes:

 Heat the milk in a small saucepan until it simmers. Mash the potatoes until smooth, taking care not to overwork them. Alternately add the butter and milk in thirds -- gently folding with a rubber spatula. Stir in the pepper.