Step 1

Combine olive oil, vinegar, garlic, oregano, salt, and black pepper in a mortar and pestle; mash into a paste.

Step 2

Make deep slits into the pork with a small knife. Stuff slits with the paste; rub any remaining paste over the pork.

Step 3

Place pork in a plastic roasting bag and put in a roasting pan with a rack. Let marinate in the refrigerator, 8 to 48 hours.

Step 4

Take pork out of the refrigerator, uncover, and bring to room temperature, 1 to 2 hours.

Step 5

Preheat oven to 300 degrees F (150 degrees C).

Step 6

Roast pork skin-side down in the preheated oven until golden brown, about 2 hours. Flip pork and continue roasting, skin-side up, until juices run clear and an instant-read thermometer inserted into the center reads at least 145 degrees F (63 degrees C), 2 to 4 hours more.