Turn on the broiler and position the rack 6-inches away from the heating element.
Place the jalapeño chiles, Hatch chiles, and garlic in a cast-iron skillet, then slide the skillet under the broiler. Cook for 10 minutes, then turn over the chile peppers and remove the garlic from the skillet. Place the garlic in the blender.
Return the skillet to the oven and continue to cook 7-10 more minutes until everything remaining is blackened.
Remove the chiles from the oven, then cover for 20 minutes so they can steam and their skins can soften.
After the chiles have steamed, peel the chiles and remove the seeds and stems. Place the chiles in the blender with the garlic.
Add the oil and salt to the blender, then puree until smooth. Taste and adjust salt, if desired.
Serve warm or chilled, either as dip or as a condiment. Will keep in the refrigerator for 1 week.