This recipe was a BUGGER to get right! I found it in a free issue of Cooks Illustrated (America's Test Kitchen). I went to three separate butcher shops and they all messed it up. I had to go back to the first one -- I didn't know what I needed well enough to tell them. But the other two?!? They like to whip it out quickly and the skin ends up tattered or missing. Or they split it for you. If you don't get the chicken right, the meat dries out. Or is impossible to remove from the bones. Or doesn't have good flavor. Or whatever. But, if you can get the chicken right -- INCREDIBLE.
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 char 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 1/2 tsp salt, butter, chipotle chiles, cumin, and cilantro 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 salt and 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.