To begin with, I use soy cream instead of dairy-based cream. It tastes alright, but not superb, and it seems to require more salt. What is missing that I should find a substitute to add back in?
By "cream" do you mean "milk?" If you are lactose intolerant, I suggest some margarine and either sour cream or yogurt. If you have a lactose allergy, still margarine, more alternate dairy products, and some kind of spice mix, like an Italian seasoning.
I made some this past week with a little olive oil (maybe 1 tablespoon?) and a little almond milk (maybe 1 teaspoon?). (I am unable to eat dairy.) I also had a rutebega mashed in--one rutebega to 4 Russet potatoes. It was delicious and even my husband, who can eat all the dairy he wants, thought they were just fine.
Mashed potatoes do not require anything to be added?
Use a fresh potato variety suitable for mashing (check with you local vegetable supplier), all you need is to mash them, and introduce some air by using a whipping process (a fork will do)
People typically add milk or cream to old or dry potatoes. Use a better potato for better results without adding anything. Reserve some of the boiling liquid to fluff up dry potatoes a little if required
I've been told that ghee has no lactose in it, so that might be one alternative to butter, but not to the milk, as I find you need some water-based liquid to get the consistency I like -- you're rupturing starch into the liquid, which gives a creamy mouthfeel.
I personally use stock, not milk to adjust the liquid in my potatoes. You have to adjust the salt, but I personally prefer it. (and it has nothing with my not being able to eat dairy.) You can add some olive oil to change the mouth feel, although too much and it's pretty obvious it's olive oil in there.
As milk is sweet, you might also consider adding a bit of other root vegetables like carrots or sweet potatoes in, but that'll significantly change the color, which the kids may not like (or they may love ... you never know). If you use carrots, you'll want to start them cooking while you're prepping the pototes, so they get a head start on the cooking, and it doesn't hurt to cut them a bit thinner.
You can add fried bacon, and be sure to include the fat rendered off while frying to compensate for the lack of butter.
If you can have butter (some people can, as the amount of lactose remaining is small), that can add a rich fattiness that soymilk sometimes lacks. Another good add-in is roasted garlic cloves, which you can mash with the potatoes -- I find even with dairy in them, that kicks the potatoes up to the next level quite handily. I usually find milk and soymilk interchangeable, but almost always add butter and/or garlic.
I have tried lactose free milk and I was surprised how good it was. I love milk. My mother not so much. She can't have dairy at all.
I go to the Asian markets, sometimes health food stores. They have a dairy free cream cheese that was surprisingly good. I use that when my mother visits. Add seasoning last so not to over-season. To thin and smooth it out, us a little of the potato water or a little soy milk. If you don't, it will be very lumpy. I didn't find just using soy milk as good.
You should check out their other non diary items. Not to shabby, some brands better then the other. Also, Smart Balance makes a margarine that is non dairy. Pretty good.