>Helen C. wrote:

>> I noticed that some use egg or egg whites. I'm curious as to why. Also
>> some recipes used sour cream, milk, cream, or yogurt. Most used
>> cheddar cheese.

Eggs or egg whites would produce a little oomph and puff to the final
product. Also, the reason to make 'twice-baked' is to encorporate the
kind of seasonings/flavorings/enrichments one would add to mashed
potatoes. What you're doing is essentially making a tasty mashed
potato mixture and cooking it in its own serving container.