Step 1: Prepare the Chiles. Carefully remove the stems from all dried chiles. For less heat, you can also remove the seeds from the guajillo and ancho chiles (leave the seeds in the arbol chiles for spice).
Step 2: Toast the Chiles. Heat a dry skillet over medium-low heat. Add the guajillo and ancho chiles first, pressing them down gently with tongs or a spatula for about 30 seconds per side, until fragrant and slightly pliable. Be careful not to burn them, as this will make your salsa bitter. Remove to a plate. Toast the arbol chiles for a shorter time, about 15-20 seconds per side, as they are smaller and burn faster. Remove and set aside.
Step 3: Hydrate the Chiles. Once toasted, place all chiles in a bowl and cover with boiling water. Let them rehydrate for 15-20 minutes, until softened.
Step 4: Toast Nuts and Seeds. In the same dry skillet, over medium-low heat, toast the peanuts, pumpkin seeds, and sesame seeds separately. Toast each until lightly golden and fragrant. Peanuts will take 3-5 minutes, pumpkin seeds 2-3 minutes, and sesame seeds 1-2 minutes. Stir constantly to prevent burning. Remove each to a separate plate once toasted.
Step 5: Fry the Garlic. Heat 1 cup of neutral oil in a small saucepan over medium-low heat. Add the peeled garlic cloves and fry gently until golden brown and aromatic, about 5-7 minutes. Remove the garlic with a slotted spoon and set aside.
Step 6: Fry the Onion (Optional). If using onion, add the onion slices to the same oil and fry until translucent and lightly caramelized, about 5-8 minutes. Remove and set aside.
Step 7: Fry the Rehydrated Chiles. Drain the rehydrated chiles, reserving a little of the soaking water. Gently pat the chiles dry with paper towels to minimize splattering. Carefully add the chiles to the hot oil and fry for 1-2 minutes, stirring constantly, until slightly crispy. Be careful not to burn them.
Step 8: Combine Ingredients in Blender. In a blender, combine the fried chiles (and their oil), fried garlic, fried onion (if used), toasted nuts, toasted seeds, apple cider vinegar, and salt.
Step 9: Blend. Blend on a low setting, pulsing rather than continuously blending, until you achieve a coarse, textured consistency. You want some pieces of nuts and chiles to remain for texture. If the mixture is too thick, add 1-2 tablespoons of the reserved chile soaking water until it reaches your desired consistency.
Step 10: Adjust Seasoning. Taste and adjust salt as needed. The flavors will meld and deepen as the Authentic Mexican Salsa Macha rests.
Step 11: Store. Transfer the Authentic Mexican Salsa Macha to a clean, airtight jar. Ensure the oil covers all the solid ingredients to preserve it well.