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1
Wash tomatillos under cold running water.
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2
Line a heavy cast iron grill pan or griddle with aluminum foil and place over high heat. Arrange tomatillos, chiles de arbol, and 2 cloves garlic in a single layer on top. Grill until chiles are blackened, turning as necessary, 3 to 5 minutes. Transfer to a bowl. Continue grilling tomatillos and garlic until they are evenly blackened, 8 to 10 minutes more.
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3
Peel garlic and place in a mortar and pestle. Season with salt and pound into a thick paste. Add chiles; pound until smooth. Add as many tomatillos as you can fit in your mortar; pound until chunky. Transfer salsa to a bowl. Repeat with remaining tomatillos, mixing them into the bowl of salsa in batches.
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4
Place guajillo and pasilla chile peppers in a saucepan, cover with water, and cook until softened, about 25 minutes.
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5
Combine softened peppers, vinegar, orange juice, 1 clove garlic, cloves, cumin, salt, and pepper in a blender; blend until smooth. Add some water if sauce is too thick. Strain into a small saucepan and bring to a simmer over medium-low heat, about 5 minutes. Remove from heat and let cool, about 5 minutes.
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6
Season trout fillets with pepper and put in a lidded container or a large resealable plastic bag. Cover with cooled sauce and refrigerate for at least 30 minutes or up to 4 hours.
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7
Remove trout fillets from the refrigerator and let stand at room temperature for 10 minutes. Remove from sauce and cut into cubes. Reserve marinade.
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8
Melt butter in a large skillet over medium heat and cook 1/2 the onion until soft and translucent, about 3 minutes. Add trout and reserved sauce; cook over medium-high heat, stirring occasionally, until trout is opaque and the sauce has been reduced, about 15 minutes. Remove from heat and fold in pineapple.
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9
Warm corn tortillas in a skillet. Divide trout mixture amongst tortillas and top with remaining 1/2 onion and cilantro. Serve with lime wedges and charred tomatillo salsa.
