Does anyone know how to make Aquamacs Command/Texing Option default to the Lualatex engine? I've checked the preferences but, so far no luck. I have the feeling this is a no-brainer and I'm missing the obvious...
Assuming you're using AUCTeX (which I think Aquamacs ships with), either of
(setq-default TeX-engine 'luatex)
M-x customize-variable RET TeX-engine RET
Digging through the AucTeX options, there is an option for setting the TeXing options in which, it is possible to choose from a list of engines then it's possible to choose the one required. Making sure to save everything at each step everything now works perfectly.