Heat the oven to 475°F.
Pour the olive oil into a small saucepan and add the minced garlic and herbs. Set the pan over high heat until the oil is hot, about 30 seconds. Reduce the heat to low and cook until the garlic has browned slightly, about 3 min. Remove from the heat and let infuse for at least 10 min. or up to 2 hours.
In a small bowl, mix together the spices, salt, and sugar.
Set the chicken on a board, breast side down, and butterfly it. Starting at the neck, remove the narrow backbone by cutting through the ribs on each side with kitchen or poultry shears. Leave the breastbone intact. Flatten the bird and turn it skin side up.
Remove the backbone by cutting through the ribs.
Press down and flatten; tuck the wing tips under the open bird.
Next, press on the breast with the heel of your hand as the bird lies flat; you'll need to break the collarbones and some ribs. Tuck the wing tips behind the shoulders.
Set the chicken skin side down in a shallow roasting pan or a jelly roll pan. Brush thoroughly with half of the garlic olive oil (use the herb sprigs as a brush, if you want, before discarding them) and sprinkle with half of the spice rub. Turn the bird over and gently loosen the skin over the breast and thighs. Brush the remaining oil and most of the spice rub directly on the flesh under the skin. Rub the remaining spices on the skin. Pierce the skin with a sharp fork or small paring knife randomly in about 10 places to help it crisp.
Roast until the skin is nicely browned and the thigh meat is 170°F or the juices run clear, about 40 min. Remove the chicken from the oven, tent with foil, and let rest for 10 min.
To serve, halve the chicken by cutting straight down the center of the breastbone. Carve each half into drumsticks, thighs, wings, and breast, and garnish on a platter with fresh thyme or rosemary, if you like.