I used a 5ml 2:1 simple syrup and a 5ml honey (not honey syrup) mixture for the honey syrup and it turned out wonderfully. The cognac, banana, and honey flavors complement each other really well.

I found it way too dry (this might be since I am in the US and so I am using Heaven Hill's American Dubonnet and not the real French kind, though HH's version has worked well for me in many other cocktails). To sweeten, I used 10 mL of a supermarket agave and caramel coffee sweetener, which fit well with the chocolatey notes from the US Dubonnet and the mezcal. Probably regular agave would have worked too.