Roast Pork Loin With Dijon Herb Crust without onion

2 tablespoons olive oil 1 tablespoon butter 2 1/2 lbs boneless pork loin roast , net removed and retied with kitchen string 1 medium onion , chopped 3/4 cup[...]

1 center-cut pork loin, with 8 rib chops (bones cracked by the butcher for easy carving later) 1 clove garlic , very thinly sliced (we use more) 2 sprigs[...]