Place the ancho and pasilla chiles in a bowl and cover with hot water. Let them soak for about 20 minutes until softened.
2 pasilla chiles, 2 ancho chiles
Pat the chicken dry with paper towels. Place it breast-side down on a cutting board. Using kitchen shears, cut along both sides of the backbone and remove it.
1 whole chicken
Turn the chicken over so it is breast-side up. Press firmly on the breastbone to flatten the chicken.
In a food processor, combine the lime juice, olive oil, tomato paste, softened chiles (stems removed), and all the spices. Blend until a smooth paste forms.
Rub the marinade all over the chicken, making sure to coat the skin well. Gently loosen the skin and spread some marinade underneath to flavor the meat.
Cover and refrigerate for at least 6 hours, or overnight for best flavor.
When ready to cook, preheat the oven to 400°F (200°C).
Wash and halve the baby potatoes.
2 lb baby potatoes
Place the chicken in a roasting pan.
Arrange the potatoes with a drizzle of olive oil, then add lime wedges, and thyme around it.
1 lime, 1 sprig fresh thyme
Cover the pan tightly with aluminum foil, sealing the edges well.
Roast for 55 minutes.
Remove the foil and return the chicken to the oven. Roast for another 20 minutes, or until the skin is golden and crisp.
Remove from the oven and let the chicken rest for 5-10 minutes before slicing.
Serve with the roasted potatoes.
Notes
Tips and Tricks
Spatchcocking tip: Removing the backbone helps the chicken cook more evenly and faster.
Marinate longer: Overnight marinating gives the deepest flavor, but even a few hours helps.
Dry the chicken well: This helps the marinade stick and improves browning.
Seal tightly: Covering with foil keeps moisture in during the first stage of cooking.
Crispy skin: Removing the foil at the end allows the skin to turn golden and crisp.
Rest before cutting: This keeps the chicken juicy and easier to carve.