How to Make It
Heat a grill pan. Add the pasilla and toast over high heat, pressing down with a spatula and turning once, until pliable and fragrant, about 1 minute. Transfer the pasilla to a heatproof bowl and cover with boiling water. Let stand until softened, about 30 minutes.
Transfer the pasilla to a blender along with 2 tablespoons of the soaking liquid. Add the vinegar, lime juice, honey and mustard and puree until smooth. With the blender on, gradually add the 1/4 cup of olive oil until incorporated. Season the vinaigrette with salt and pepper.
In a large skillet, heat 2 tablespoons of the olive oil until shimmering. Add the onion and cook over moderately high heat, stirring occasionally, until softened, about 5 minutes. Add the beans and achiote and cook, stirring, until fragrant, about 2 minutes. Add the stock and cook until the beans are hot and glazed, about 3 minutes. Stir in half of the vinaigrette and the chopped cilantro. Season with salt and pepper and keep warm.
Heat the grill pan. Brush the steak with oil and season with salt and pepper. Grill over high heat, turning once, until lightly charred, about 6 minutes. Transfer to a carving board and let rest for 5 minutes.
Meanwhile, brush the scallions with oil and season with salt and pepper. Grill over high heat, turning, until lightly charred, 1 to 2 minutes. Thinly slice the steak against the grain and serve with the beans and scallions, passing the remaining vinaigrette at the table.
Pasillas are long, black dried chiles with a fruity, herbaceous flavor. They are available at Latin markets.