Start by peeling and chopping the russet potatoes into 1-inch chunks. This ensures even cooking and a uniform texture.
Place the chopped potatoes into a large pot and cover them with 2 inches of water. It's important that the potatoes are fully submerged to cook evenly.
Bring the pot to a boil over high heat. Once it reaches a boil, reduce the heat and let it simmer. Cook until the potatoes are fork-tender, which should take about 10 to 15 minutes.
Once tender, drain the potatoes in a colander and let them sit for 5 minutes. This helps steam off any remaining moisture.
While the potatoes are steaming, add the heavy cream, whole milk, and butter to a medium saucepan. Heat over medium heat until the mixture is warm and the butter has completely melted.
Next, return the drained potatoes to the pot (or a large mixing bowl) while ensuring the heat is off. Mash with a potato masher until smooth.
Now, slowly add the warm cream mixture to the mashed potatoes. Stir gently until combined, ensuring you don't overmix.
Season with Kosher salt and freshly ground black pepper to taste.
For serving, transfer the mashed potatoes to a warm serving dish.
