Part 1: Cooking the Potatoes

Step 1: Peel and Cut Consistently
Peel the potatoes. For Yukon Gold potatoes, cut them into 1-inch thick slices. For denser Russet potatoes, cut them into 1-inch cubes. Uniform size is crucial for even cooking.

Step 2: Start in Cold, Salted Water
Place the cut potatoes in a large pot and cover with cold water by at least an inch. Add 1 tablespoon of kosher salt to the water. Starting in cold water ensures the potatoes cook evenly from the outside in.

Step 3: Boil Until Tender
Bring the pot to a boil over high heat. Once boiling, reduce the heat to maintain a gentle simmer. Cook for 15-20 minutes, or until the potatoes are very tender. They should offer no resistance when pierced with a fork or paring knife. Do not undercook.

Step 4: Drain and Dry Thoroughly
This is a critical step for fluffy mashed potatoes. Drain the potatoes in a colander. Then, return them to the empty, hot pot over the turned-off burner. Let them sit for 1-2 minutes, gently shaking the pot, to allow any residual surface moisture to evaporate. Wet potatoes become watery, gluey potatoes.

Part 2: Preparing the Warm Dairy

Step 5: Heat Milk and Butter
While the potatoes are draining, combine the milk and cubed butter in your small saucepan. Heat over low until the butter is melted and the mixture is warm to the touch (about 150°F / 65°C). Do not boil. Warmed dairy prevents the potatoes from cooling and seizing up, leading to a smoother incorporation.

Part 3: Mashing and Seasoning

Step 6: Rice or Mash the Potatoes
For the smoothest, most luxurious texture, pass the hot, dry potatoes through a potato ricer or food mill back into the pot. If using a hand masher, mash until no large lumps remain. Do not use a food processor or blender, as they will release too much starch and create a glue-like texture.

Step 7: Incorporate the Dairy
Pour about half of the warm milk-butter mixture over the riced potatoes. Using a rubber spatula or a wooden spoon, fold gently to incorporate. Add the remaining dairy gradually until you reach your desired consistency. The potatoes should be smooth and creamy but still hold their shape.

Step 8: Add Enrichments and Season
If using, fold in the room-temperature cream cheese until fully blended. Now, season aggressively. Start with 1 teaspoon of salt and a generous amount of pepper. Taste thoughtfully. Remember, potatoes are a blank canvas and require ample seasoning. Add more salt and pepper in small increments until the flavors sing.

Step 9: Final Whip (Optional)
For an extra-light, whipped texture, use a hand mixer on low speed for 30-60 seconds. Be careful not to overmix.

Step 10: Serve Immediately
Transfer the mashed potatoes to a warm serving bowl. Make a well in the center and add a final pat of butter for presentation. Serve immediately.