So, I’m late (well, two days – not as bad as it could have been!) with the muffins, but I really wanted to make these. My family is a big fan of muffins (and scones), so this seemed like a natural fit. Well, they’re good. Not great. Not spectacular but they are good. I think next time I’ll make them either with a combination of shortening and butter or all butter – there’s something about the flavor of a muffin made with butter! I am somewhat flummoxed, though – I’ve never had a muffin sink in the center (well, under baked, not withstanding). Oh, yeah – and I would make them again.
scaryladyatho 
I am really curious as to why so many bakers had this problem. This is one recipe that needs tweeking.
I think sometimes too much leavening leads to this issue of sinking? I vaguely remember an ATK article about that! A mix with butter sounds good!