4 Tbsp. olive oil, divided
1/3 C. finely chopped onion
1 lb. fresh Italian sausage (hot or sweet) casings removed
½ C. panko or coarse bread crumbs
2 Tbsp. fresh chopped basil
4 lb. center-cut boneless pork loin
2 Tbsp. chopped fresh rosemary
Mansmith’s Crusting Rub
In a large skillet, heat 1 Tbsp. oil to medium high. Add onion, and cook, stirring. Crumble sausage into skillet and cook, breaking up with fork until browned, about 5 minutes. Stir in panko and basil, cook one minute more. Let cool then finely chop.
Rinse pork and pat dry. Cut 3 inch deep horizontal slit down center of pork. Leave ½ inch uncut at each end. Stuff sausage mixture into pocket. Tightly tie with kitchen string to enclose stuffing. Generously season with Crusting Rub. In a small bowl, combine remaining oil and rosemary, spread over pork. Wrap meat with plastic wrap to make an air-tight seal. Place in container, cover with more plastic wrap and refrigerate 4 hours or overnight.
Unwrap and let pork stand at room temperature while preparing the grill. Heat grill to medium. Grill pork, turning every 10 minutes until thermometer registers 145ºF at center (25-30 minutes). Roast in oven at 450ºF for 50-60 minutes. Let stand 5 minutes before slicing.