From the kitchen of: America's Test Kitchen (maybe)
Good mashed potatoes just are.
2 lbs Potatoes, peeled, quartered, and cut into 1" cubes
1. Place potatoes in a pot and cover with 1 inch of water.
2. Bring to a boil, then reduce heat and simmer. Cook until potatoes are tender and a paring knife can be inserted into potatoes with no resistance. 20-25 minutes.
3. Drain in a colander.
4. Put potatoes in mixer and add butter. Mix until just incorporated.
5. Fold in 3/4 cup half-and-half. Add remaining half-and-half as needed.
6. Add salt and pepper.