I swear by lots of merino wool. I usually have on a merino base layer (top & bottoms), light wicking turtleneck and warm wool sweater. Merino ski or snowboarding socks. Jeans (but you could substitute biking pants), and a windbreaker. If it is really cold (single digits to 20 or so below zero), I have a down sweater that fits under my windbreaker. I wear a merino buff as a balaclava and have a merino beanie under my helmet. Warm mittens and goggles completes the ensemble. I look a bit odd, but warmth is important.

Deb