A few years back, I signed up for America's Test Kitchen (which I HIGHLY recommend). With my subscription comes a year's worth of magazine's from Cook's Illustrated. I haven't made it past the first recipe -- because it's so good and I had to try the variations. This chicken turns out so tender and moist and flavorful! The trick is finding a butcher (or learning for yourself) that will cut the bird properly. See my notes!
First, the chicken: this recipe relies entirely on the breast bone still attaching both breasts together and the skin needs to be still attached. Either cut a whole chicken yourself (and don't destroy the skin!), or have a butcher do it, but WATCH THEM -- don't accept a split breast or tattered skin! Also, it's confusing, but you need TWO -- that is, two chest pieces (two separate birds).
Adjust oven rack to middle position; heat oven to 450*F. Line bottom of broiler pan with foil; place broiler pan rack on the top and set aside.
In a small bowl, mix butter, 1/2 tsp salt, garlic, rosemary, and lemon peel until combined.
Sprinkle underside of chicken with salt and pepper.
Carefully lift the skin from the meat, coming in from one edge. Try to keep the edges attached, as much as possible -- a 2" hole should allow you plenty of room to work. Carefully maneuver half of the butter mix under the skin and smooth over the meat. Repeat for the other chickie. Smooth the vegetable oil over top of the skin of both and sprinkle liberally with pepper.
Set both on broiler pan. Roast until thickest part of breast registers 160*F, 35 - 40 minutes.
Transfer chicken to cutting board and let rest for 5 minutes. Split the breast by coming down the middle and sliding knife along the breast bone and over the ribs (much easier said than done). Serve immediately.