• Peel and dice potatoes into even 1 1/2-inch cubes; cover with water and reserve.
• Place potatoes in a large saucepot, add salt and bring to a boil; simmer until just done. (Tip of knife easily penetrates the potato, but it does not fall apart.) Drain very well in colander.
• Heat cream in small saucepot to just below simmer; reduce by half, season with salt and pepper, and begin sieving potatoes through fine mesh screen or ricer into the sauce pot with the cream on a low flame burner, adding the butter as you go.
• Remove from heat, check seasoning and reserve warm until ready to serve.