I recently got a great price on a pair of Hestra Heli Mitts, I have to give them a big thumbs up (pun intended). They have removable liners and the liner gloves that go with their Heli Gloves will also velcro into the mitten shell.

They are really well made, warm, and comfy, I can't imagine needing another mitten system anytime soon. As luck would have it, I'm going to have the opportunity to test them in some single digit temperatures next week...