Preheat your oven to 450 °F. Then, scrub the potatoes and prick them with a fork several times.
Place the potatoes directly on the middle oven rack and bake for 60 minutes or until they are very soft and squishy when squeezed with an oven mitt. You do not have to use a baking sheet.
Right before the potatoes are done, add the cream and three tablespoons of butter, plus the salt and pepper, to a small saucepan and bring it to just below a simmer over low heat. Do not let the mixture boil.
Remove the potatoes from the oven. Working quickly to keep them as hot as possible, cut them in half horizontally, one potato at a time, and then use a kitchen towel or oven mitt to hold the halves while you scoop out the flesh into the bowl of a stand mixer. Put a kitchen towel or a sheet of aluminum foil over the top of the bowl while you are working to keep the potatoes hot while you repeat this with the rest of the potatoes.
Use a potato masher, potato ricer, or fork to smooth out the potato flesh and remove as many lumps as possible.
Then, using your paddle attachment, beat the potatoes at low speed just until they are smooth. Do not over-mix or overbeat them.
Add the cream and butter mixture to the potatoes and gently fold it in with a rubber spatula. Don't panic; it will look like you have too much cream, but be patient and keep gently folding until the warm potatoes have absorbed all of the warm cream and butter. Taste and add additional salt or pepper, if needed.
At this point, they are ready to serve. However, if you are making them ahead, place the mashed potatoes in a 9' x 9' inch metal baking pan that has been sprayed with non-stick cooking spray and spread them out evenly. Cover with aluminum foil and store in the refrigerator for up to 48 hours.
Before serving, bake or reheat them covered in a 350 °F oven for 20 to 30 minutes or until they are hot. Place in a serving dish, add a pat of butter, and serve immediately.
Notes
Because the potatoes are baked and not boiled in salted water, they may need a bit more salt. Be sure to taste them before serving and add salt if needed.
When the potatoes go into the fridge, they might still be a little looser than you like. However, they will firm up when they are chilled.
Feel free to garnish this dish with chopped chives, cooked crumbled bacon, or shredded cheese before serving.
For perfect mashed potatoes, the most important thing to remember is to work quickly and keep them as hot as possible when scooping out the insides and mashing them.
Also, ensure that your cream and butter mixture is hot before adding it to the hot potatoes. If they get cold, you won't be able to get the lumps out, and the cream will not be absorbed.
After reheating the mashed potatoes in the oven, if you still need to keep them warm or travel with them, put them in a crockpot or slow cooker on low or warm. They will keep well like this for several hours.
Less is best! Overmixing or over-processing with a mixer, blender, or food processor can cause mashed potatoes to go from fluffy to gummy in the blink of an eye.
Leftovers can be stored covered in the fridge for up to four days. I do not recommend freezing them.
To reheat them, pop them in the microwave for 30 to 60 seconds or until they reach your desired temperature.