That's where I've been struggling a bit as well.
If I dress to be comfortable for the majority of my ride I end up a bit warm in the beginning with the 3 mile hill I need to concur... so I need to pace it a little slower than I prefer so I don't overheat. The rest of the 25 ride is pretty comfortable if I don't stop. But there's a nice park where I like to stop at around mile 14 and have a piece of fruit and some chocolate espresso beans. When I start back everything is cold, especially my fingers and it's hard to get them warm again.
This year I'm trying this and it's working better

They are much warmer than any full winter skiing glove I've ever tried and things are easier to control as you can wear summer time open finger gloves under the muffs.
When I stop for my break I throw these inside and fold the ends over to retain the heat.

The hand heaters aren't necessary unless I stop for a break but when I do and then resume the interior is warm and comfortable.
Downside of this is...
They can be a bit cumbersome, especially handling the bike when not riding.
They are a few minutes work to put on/off early in the season when you might not need them for every ride. Especially since I popped a hole in the left one for the bar end mirror and have to fold the bar end horns down... but even then it's only a 5 minute task.
I can't really use my bell as it sits outside the muffs but I have my wired in horn easily accessible and controlled from within the muffs. That said I need a bell a lot less in the cold as there are far fewer people out.
Can't say I'm in love with them... But they are definitely the warmest solution I ever tried. So far they've worked very well down to 38°f and with a lot of wind... and I'd estimate they can handle 30°f no problem still using open finger gloves underneath.
The pair I purchased were less than $10 and not the greatest quality and if I'm happy with them at the end of the season I may look into something made a little better. I wasn't sure if I'd find them comfortable in use and I knew I was going to cut the mirror hole in them so I went cheap to test out the theory.
So far they're a keeper.
y°fmv