Prepare the potatoes: Peel the russet potatoes and cut them into even, 1-inch chunks. Place them in a large pot and cover with cold salted water by about an inch. Starting with cold water ensures the potatoes cook evenly from the inside out.

Cook until tender: Bring the water to a boil over high heat, then reduce to a simmer. Cook the potatoes for 15-20 minutes until they are fork-tender - a fork should easily slide in and out. Drain thoroughly and return the potatoes to the hot pot. The residual heat will help evaporate excess moisture.

Prepare the cream mixture: In a small saucepan, gently heat the milk, heavy cream, and butter until warm but not boiling. Add the softened cream cheese and stir until completely smooth and incorporated. This warm mixture will blend more easily into the potatoes.

Mash and combine: Using a potato masher or ricer, mash the potatoes until no lumps remain. Gradually add the warm cream mixture, incorporating a little at a time and stirring gently. Continue until you achieve your desired consistency - the potatoes should be smooth and creamy.

Season and serve: Season generously with salt and freshly ground black pepper to taste. Transfer to a serving dish and top with optional garnishes like a dollop of sour cream and fresh thyme sprigs for extra flavor and visual appeal.