Cycle.Travel suggested route, which I have mostly ridden (from Nazeing north).
I recommend this route. It begins with canal towpaths and progresses to ever-lovelier countryside, before the flat, glorious run-up to Cambridge.
I have not ridden between the A110 (at the immediate start) to Nazeing, but this hopefully isn't as busy as the route suggested here: http://rides.tomtaylor.co.uk/routes/london-cambridge.html - which uses the incredibly busy A110, A112, and B114 all the way up to Nazeing Common (where I abandoned it). These roads have barely any shoulder, no cycling facilities, and very fast traffic - even though some aren't even B-roads.
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Update: I've now ridden this entire route, and can thoroughly recommend it.
It's entirely quiet roads, well-paved cycle lanes, or canal towpaths (which can admittedly be a little bumpy in places, but nothing a road bike can't handle).
If heading north, be aware that (because of those towpaths) you may take nearly half the time to reach Ware. After that, it's quiet roads or paved cycle paths the entire way.
There are a few minor climbs - not least in Ware itself - but nothing insurmountable or even difficult.
Good stopping points for food: The Fish and Eels (just after you cross Dobb's Weir Road); also, The Catherine Wheel, on Albury Road.
There's also a handy convenience store on the High Street (B1004) in Much Hadham: https://goo.gl/maps/bEh43gUiqNt