I make all my own cables now. I buy the Venhill clutch kits and the appropriate size nipple to suit British handlebar levers and own one of their bird cage tools which does a fat better job than just flaring the ends of the cable which can still pull out.
I make a solder pot using a stainless measuring cup filled with a reel of plumbers type solder and heat it on a camping stove. After fluxing the cable I can sit the end in the solder for a minute and keep dunking until the nipple is sufficiently
Filled with solder. Being careful not to dunk the nipple in too far and soldering the wire past the nipple which is what will cause the cable to eventually break.
The Venhill kits are also Teflon lined which makes them a lighter and smoother action as well as having a heavy duty outer.
The Venhill bird-caging tool is excellent, and the Teflon-lined outers are nice as well.
I use tinman's solder rather than plumber's solder, and a soldering iron which makes the lights dim when I turn it on. The solder pot seems like a good idea.
To do it better than original, the trumpet nipple + matching barrel nipple combination should be worth experimenting with.
David's silver solder approach seems intriguing as well, but may be overkill.