Do you need to put the butter on *before* removing the tin foil?
In the video you say you can store the tin foil on top and reuse it, but isn't there butter all over it? Can you wait to put the butter on until you remove the tin foil, or is the butter helping somehow to keep the moisture in the sweet potatoes? You say the butter needs to start caramelizing, but can that happen in the last 20 minutes?
Also, you mention that some people have roasting pans with lids? Any links to such a pan? I've never seen one.