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1
Heat ancho chilies in a medium saucepan over high heat, turning occasionally, until toasted and fragrant, about 3 minutes. Transfer to a microwave-safe measuring cup and cover with 1 cup water. Microwave on high heat until just simmering, about 3 minutes. Let steep until chilies are softened. Drain chilies, reserving liquid.
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2
Meanwhile, heat 1 tablespoon oil in now-empty skillet over medium-high heat until shimmering. Add onions, and cook, stirring frequently until softened and lightly browned, about 8 minutes. Add garlic and oregano and cook, stirring frequently, until fragrant, about 30 seconds. Add vinegar, chipotle chili and sauce, and reserved chili liquid. Scrape up browned bits from bottom of pan. Transfer contents to jar of a blender along with soaked chilies, sour cream, and lime juice. Blend on high speed until completely smooth, about 1 minute. Season to taste with salt and pepper and set aside.
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3
Heat remining tablespoon oil in a large skillet over high heat until smoking. Add asparagus, season with salt and pepper, and cook without moving until well charred on bottom, about 2 minutes. Toss and repeat, allowing asparagus to char before tossing again. Repeat until all asparagus is charred and softened, 8 to 10 minutes total. Transfer to a large plate.
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4
Form 12 double stacks of tortillas. Spread a tablespoon of sauce over each one. Divide asparagus evenly between tortillas. Top with pickled onions, cheese, and cilantro. Serve immediately with lime wedges and extra sauce.
