Peel the potatoes with a vegetable peeler. As soon as you peel a potato, add it to a bowl of cold water. Once you’ve peeled them all, drain them and cut them into large chunks.
To a large pot, add the potato chunks, cover with cold water by about 1 inch over, and add 1 tbsp of kosher salt. Bring the water to a boil over medium-high heat, and turn it down to a simmer once the water is boiling. Continue simmering until the potatoes are tender. It will be about 10 minutes to bring to a boil, and then 15-20 minutes of simmering time, more or less depending on how big the chunks are. Check if the potatoes are cooked by inserting a knife through the middle of the biggest chunks. If the knife goes in and out easily, then they are fully cooked.
Drain the potatoes, reserving 1 cup of the starchy potato water. Mash the potatoes (ideally passing them through a potato ricer). If you don’t have a potato ricer, you can use a potato masher. If using a potato masher, avoid overmixing the potatoes so they don’t get gluey.
Warm up the milk, cream, and butter in a small pot over the stove over medium heat, stirring frequently so the bottom doesn’t burn, until the butter has melted. Add the mixture to the mashed potatoes in stages, mixing with a spatula to combine.
After incorporating the milk, butter, and cream into the mashed potatoes, add some potato water if you want to adjust the consistency. I use about 1/4 cup of potato water for the consistency you see in the photos. Taste the potatoes and add more salt to taste.