I have been the unofficial mashed potato maker for the last 35 years or so. Somehow my childhood fascination with the potato ricer ("it squirts out worms!") meant that it became my job, and if I didn't do it, no one else would. I really like mashed potatoes, so as a result, I am pretty good at it.
While I was in CA over break I visited Judy. She had an ultra-rich mashed potato recipe she wanted to try. I made the potatoes while she made the main course. For 5 lbs of potatoes, it had an 8 oz package of cream cheese, 2+ sticks of butter, and some half and half. Yeah, that does sound good. I made a half recipe. It was quite tasty, but somehow it did not live up to the promise imparted by so much butter. (Perhaps we did not add enough butter? I didn't exactly follow the recipe, and added less butter than they called for, since we ran out, but it was still a lot and I added proportionately more cream cheese to make up for it.) In fact, I realized I like my mashed potatoes better, even though they're practically diet food compared to that recipe. Unfortunately, they're not really diet food so I don't make them for myself that often.
My recipe is neither CI-compliant (oh noez, I didn't roast the potatoes and then mash them!!!), nor over the top food-blogger compliant (what - only 3 tbsp of butter!?!? you didn't roast the garlic?), nor diet food blogger compliant (OMG - too many carbs!). But it is easy and good, and you can feel good about not paying $8.49 a lb for pre-made mashed potatoes at Wegman's or Whole Foods. However, if you are feeling lazy I will be happy to sell them to you at that price.
Anyway, my secrets are not so secret. I cook the potatoes in broth, and then use mostly the brothy potato water when I am mashing them, rather than milk or cream. I add some butter and milk or half and half, but not too much. I used to use more milk/cream/butter and less broth, but one time when I made them extra light I got lots of unanticipated compliments. Lastly, I add peeled garlic cloves to boil with the potatoes and mash them right in. If I'm bringing them for a Thanksgiving dinner I'll increase the amount of butter and use half and half, but even then they're not super rich.
Big bowl o' mashed potatoes (intermediate richness level, amount of milk and butter are estimated)
2.5-3 lbs russet potatoes
32 oz broth (chicken or vegetable)
3 garlic gloves, or to taste
1 cup milk
3 tbsp butter
salt and pepper
reserved potato water
Wash and peel potatoes. Cut into chunks and add to soup pot. Add broth, garlic cloves and enough water to cover potatoes. Boil until potatoes are tender. Scoop out potatoes and a bit of the liquid and mash -I use my stand mixer, but a ricer or potato masher is fine too. Add butter, milk and enough potato broth to get them to your preferred texture. I like them moist and fluffy so I add a lot. Add salt and pepper to taste. You can make them in advance and then reheat in the oven or microwave.