2 pasilla chiles, stemmed, seeded, deveined, and torn into small pieces
2 ancho chiles, stemmed, seeded, deveined, and torn into small pieces
1/2 cup dried whole oregano (preferably Mexican)
2 tablespoons onion powder
2 tablespoons garlic powder
1/4 cup Spanish paprika (pimento)
Heat a dry skillet over medium-low heat. Pour in the cumin, coriander, fennel and mustard seeds along with the pieces of pasilla and ancho chiles. Toast, stirring constantly, until aromatic and just begins to smoke, about 3 minutes.
Dump the mixture onto a plate and let it cool to room temperature. Grind to a fine powder in a spice grinder or clean coffee grinder. Transfer powder to a large bowl and add the oregano, onion powder, garlic powder and paprika. Stir well to combine. Store the adobo in an airtight container or resealable plastic bag in a cool, dark place for up to a month.