I've got a guest allergic to dairy
Use 1/4 -1/2 great quality olive oil for every 2 lbs of potatoes instead of the dairy - it's delicious. You can add garlic cloves to the boiling water and mash them along with the potatoes for added flavor.
Here's another trick, to boost the flavor: Caramelize a whole mess of onions, and then blitz them in the processor with some olive oil. Stir this puree into the mash.
You can also roast the garlic for a deeper flavor - just trim off the top of a bulb, give a good drizzle of extra virgin olive oil, wrap in foil and roast on 400 40 min to an hour.