How to Make It
Preheat the oven to 400°. In a food processor, combine the butter with the chopped onion, the chili powder, garlic, citrus zest and juice, honey, cumin and 1 tablespoon of salt; puree until smooth. Loosen the chicken’s breast and thigh skin; spread three-fourths of the butter under the skin. Rub the remaining butter over the chicken and let stand for 30 minutes.
In a medium roasting pan, toss the potatoes with the poblanos, jalapeño, sliced onion and the olive oil and season with salt and pepper. Open the can of Dr Pepper and nestle it in the center of the roasting pan. Stand the chicken upright on the can and roast in the center of the oven for about 30 minutes, until lightly browned. Reduce the oven temperature to 325° and roast the chicken for about 45 minutes longer, until an instant-read thermometer inserted in the inner thigh registers 155° and the vegetables are tender. Let rest for 15 minutes, then transfer the chicken to a carving board. Discard the soda.
Remove the meat and skin from the chicken and shred. Add the shredded chicken and skin to the roasting pan and toss with the vegetables. Cover with foil and keep warm.
In a medium skillet, heat 1/4 cup of canola oil until shimmering. Add 1 corn tortilla and cook over moderately high heat until pliable, about 20 seconds. Fold the tortilla in half and fry, using tongs to prop it open and turning occasionally, until a crisp shell forms, 1 to 2 minutes longer. Transfer to a paper towel–lined baking sheet. Repeat with the remaining corn tortillas, adding more oil as necessary.
Heat a large cast-iron griddle over moderate heat. Place 2 or 3 flour tortillas on the griddle and scatter 2 scant tablespoons of the cheese and 1 tablespoon each of the beans and white onion on top. Cook over moderate heat until the cheese is melted, 1 to 2 minutes. Working quickly, wrap a crispy corn tortilla in a flour tortilla, pressing gently to help it adhere. Repeat with the remaining flour tortillas, cheese, beans and white onion.
In a bowl, whisk the sour cream with the lime juice; season with salt. Fill the double-decker taco shells with the chicken and vegetables. Serve with the lime cream, salsa, avocado, cilantro and lime wedges.