Serrano chiles look like this:

those are ripe and look like they’d be hot (they’re from Ojai, CA, so I doubt they’ve had the rain to sweeten them).

Piloncillo and/or Domino’s dark brown sugar

On a national scale, Melissa’s, of California, makes it; in Texas I like the “store brand”. You can if need be find it in Mexican markets or online (amazon has some), but this

.

works as well if you can find the dark. I haven’t tried the “brownulated,” but if you have Albertson’s stores they may carry a “sugar in the raw” or an English version of “turbinado” sugar in the bakery section. Interestingly, this is the sugar recommended for homemade ginger beer:
Happy Herbalist.