Place habaneros and arbol chilies in a bowl and cover completely with warm water. Weigh down with a plate to keep peppers fully submerged. Soak overnight (8-12 hours).

Heat vegetable oil in a large skillet over medium-low heat. Add Roma tomatoes and whole head of garlic to the oil.

Cook tomatoes and garlic in the oil for 15-20 minutes, turning occasionally, until tomato skins begin to peel and loosen naturally. The garlic should become golden and soft.

Remove tomatoes and garlic from oil and let cool slightly. Discard the cooking oil (do not add to salsa).

Drain the soaked peppers and remove stems. For less heat, remove seeds from some or all peppers.

Squeeze roasted garlic cloves from their skins. Peel the loosened skin from tomatoes.

Add soaked peppers, roasted tomatoes, garlic, raw onion, oregano, and salt to a blender.

Blend until desired consistency is reached, starting with short pulses and gradually blending longer for a smoother texture.

Taste and adjust salt and heat level as needed. Let salsa rest for at least 30 minutes before serving to allow flavors to meld.