Add chiles, tomato, and garlic to a medium sauce pot and cover with water. I use about 1.5L/qt for my 3qt pan.
Bring mixture to a boil over high heat. Once it's boiling, stir and press chiles to submerge, cover the pot, and allow to soften off heat for 15 minutes.
Add softened chiles and tomatoes into a blender along with 300-350g/mL of the chile cooling liquid. Blend on high until very smooth.
Drop the pan you used for the chiles back over medium heat with a squeeze of olive oil, onion, and a large pinch of salt. Cook the onion until softened.
Add in the chile puree along with cider vinegar, sugar, and salt. Stir and cook for 15-20 minutes, stirring occasionally, until reduced by about 50%. Taste for seasoning and adjust with salt, sugar, or vin if needed.