I know that these are not supposed to be like mashed potatoes, but I did cut back considerably on the milk (to about 1/3 cup). I think my potatoes were a little less than 14 oz total weight as well so a cup of milk would have resulted in potato slush rather than silk. The first time I made them I didn't put them in the food processor--you can tell by the first photo that they're not nearly as appealing. I made them again and did use the food processor and they were beautiful in appearance and taste.
I didn't have white truffle oil but I did have white truffle butter on hand so I substituted that. Texture was creamy, even silky, potatoes were delicious! Everyone loved them! I did have to boil the potatoes a bit longer than specified. Great recipe!