In reply to Jerry67:
Hestra mitts are my glove of choice although not waterproof (some are however), but you can change the liners easily. The thing I like about Hestra gloves generally is they come in more sizes. Not just S,M,L but sizes 1 to 11. I take a size 9, which is between M and L and therefore gives good warmth to dexterity ratio. They have leather palms and are quite soft compared to BD.
Another alternative is the Lobster type glove / mitt. I use ones by Black Diamond, they are very well made and have a thinner palm glove that gives better dexterity (although if walking in -15 you do get cold inner hands. Hestra make a lobster glove / mitt that is softer than the BD.
I have also a pair BD mercury mitts, warm and not very dexterous and not so good with rope handling. i mainly use them for dogsledding.
To be honest the best mitts I have are the ones my wife's aunty made for me a few Christmases back. They are thicker than Dachstein Mitts and have a cool pattern on them, when paired with an outer glove keep my hands warm to -15 and more. Stay warm when wet. The dogsledders I know mainly use woolen mitts, and when really cold two pairs with just a cotton outer.
Needle sports website has a good selection of mitts for sale.