My hubby loves shepard's pie! I've never made it with mince, that's just something available here, but I use ground beef, pork, or turkey - it all works. Now I love sweet potatoes, him not so much, but I think the mix of butternut squash and sweet potatoes would be divine.
Well I suppose hon, ground beef is pretty much the same thing - just not quite as juicy and tender as mince so nothing wrong with that! As for the mix - yes! that is precisely why I do it because it completely transforms the traditional "sweet potato" taste! Hope you try it xxx