Add the potatoes to a large pot and cover with cold water. Add a large pinch of salt. Bring to a boil, reduce to a simmer, and cook until tender, about 25 minutes. Drain well in a colander.
Add the butter, shallot and milk to the same pot the potatoes were cooked in and heat until the butter is melted and hot; season well with salt and pepper. Remove from the heat.
Add the potatoes to the hot milk and butter mixture. Add the sour cream. Using a potato masher, mash the potatoes until semi-smooth. Add the cheese and stir until the cheese is incorporated. Adjust the seasoning as necessary.