If you have the time, salt the chicken liberally and store uncovered for several hours or overnight on the lowest shelf of the fridge. Salting the chicken several hours in advance produces extra crispy skin and very moist meat. Pat the chicken dry before roasting.
Preheat oven to 425°F.
Toast cumin seeds in a small pan over moderate heat until fragrant. Place in a mortar and pestle or spice mill and grind the seeds to a powder.
To spatchcock a chicken (or any poultry), place the bird breast-side down on a cutting board with its wing tips facing up and away from you. Feel down the back of the bird to find the spine then, using poultry shears or kitchen scissors, cut up and along the spine on each side. Remove the backbone and discard or save it to flavor a chicken stock.
Flip bird over, breast-side up. Place your hands at the center of breast and press down to crack breastbone and flatten the bird. Trim the wing tips and discard or save for stock as well.
Place the chicken on a wire rack set on a rimmed baking sheet. Drizzle with EVOO and season with salt (skip the extra salt if the bird has been salted and resting in fridge), pepper and half of the ground cumin.
Roast chicken 45-50 minutes, until it reaches an internal temperature of 165°F and the juices run clear.
Place the skillet you toasted the seeds in back over high heat with a drizzle of oil and the limes, cut-side down. Caramelize the limes to make the juice sweeter and more concentrated; let cool.
Place about 1/4 to 1/3 cup of EVOO (pour slowly to a count of 6) with the juice of the 3 limes. Season with salt and pepper, crush and remove skins from 2 large cloves garlic and add to blender along with the remainder of the cumin and the leafy tops of a large bunch of cilantro or parsley.
Cut the top off of the jalapeño pepper, split the pepper lengthwise and remove its seeds and ribs with small paring knife. Add the jalapeño to the blender and blend on high for 2 minutes or until very smooth and bright green. Taste to adjust seasoning.
Place chicken on a carving board, slather the mojo sauce evenly over the bird and serve.
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