-Milk will work if you don't have buttermilk.
-I bake my potatoes in the oven. Wash, dry and pierce with a fork. Place on a baking sheet and bake for 30-45 min at 375 degrees or until it passes a fork test. Let them cool, then peel the skin off or cut open and scrape out the insides. I have also peeled, cut up and boiled the sweet potatoes till they pass a for test. You could also use canned yams if you were pressed for time. I use salted butter, if you prefer unsalted, add a ½ tsp. salt to the potato mixture.
-You can use less sugar if you prefer your sweet potatoes not so sweet. I have made these with ½ cup sugar and it was still delicious!
UPDATE 11-11-14: I recently made this for a pre-Thanksgiving dinner. I added a little more sweet potatoes (probably a ½ cup. A total of 4 medium sized) I didn't adjust the recipe other than that, but I baked in a 13x9" pan and it worked great! It was a for a large sized group so I wanted it to go farther and there wasn't a bit leftover :) It makes the crust not as thick but nobody seamed to mind.