Method
Pat the quesadillas dry and season generously with salt and pepper.
Sear in a hot pan with vegetable oil until deeply browned on all sides, then set aside.
Soften white onion and serrano chili in the same pot, scraping up the browned bits.
Return everything to the pot, add liquid to barely cover, and braise low and slow until fork-tender.
Reduce the sauce until glossy, adjust the seasoning, and finish with fresh herbs.
