At Thanksgiving, I use an entire bag of red potatoes, cut into small chunks and boiled with some sea salt. When the potatoes are fork tender, drain them (retaining some of the liquid). Add a stick of butter, plop in some milk, toss in some more sea salt and pepper, and mash away until the potatoes are perfect.
At other times, I simply use as many red potatoes as I feel are necessary and adjust my non-measured ingredients above. Sometimes I will even throw in some sour cream or cheddar cheese or roasted garlic to make them all more spiffy. My rule of thumb--keep the skins to save the work (and the fiber and nutrients) and doll up the potatoes to taste! (Not very helpful in a recipe cloud, I realize...)