brick wrapped in aluminum foil or heavy cast iron skillet
Open chicken flat like a book; place butterflied chicken, skin side down, on rimmed baking sheet or casserole dish. Mix 2 tbsp. lemon juice, 2 tbsp. oil, 1 tbsp. chopped rosemary, and garlic in a small bowl. Rub mixture all over both sides of chicken. Cover and chill overnight.
Preheat oven to 400 F. Sprinkle chicken with coarse salt and freshly-ground black pepper. Heat remaining 1 tbsp. oil in large ovenproof skillet over medium-high heat. Add chicken, skin side down, to skillet and cook until golden brown, about 7 minutes (do not turn chicken over).
Place foil-wrapped brick (or cast iron skillet) crosswise across chicken; roast in oven 30 minutes.
Remove brick and turn chicken over; return brick to chicken and continue to roast until juices run clear when thickest part of thigh is pierced, about 15 minutes longer.
Remove brick and transfer chicken to platter. Drizzle chicken with remaining 2 tbsp. lemon juice and sprinkle with crushed red pepper and parsley.