Peel 3 lb russets chef's knife cutting board. Quarter large chunks even 2-inch pieces. Large pot cold water cover add 1 tsp salt. Boil high heat lid off 20 minutes fork tender soft center.
Colander drain hot potatoes shake dry. Return empty pot heat off. Rice potatoes 1 minute wooden spoon shake steam escape no water weight.
Saucepan warm 1 cup milk ½ cup butter low heat melt smooth no boil. Pour hot over potatoes pot. Sprinkle 1 tsp salt ¼ tsp pepper.
Potato masher smash chunks coarse first. Wooden spoon stir milk butter fold 2 minutes silky lumps gone steam hot. Taste salt adjust pepper pinch. Serve steaming fluff.