I bought a big pork roast the other day without the slightest clue how I wanted to cook it. So I turned to Mark Bittman, because he's never steered me wrong.
from How to Cook Everything
4 cloves garlic, peeled
1 medium onion, quartered
2 Tbsp. fresh oregano, or 1 Tbsp. dried
1 Tbsp. salt
2 tsp. freshly ground pepper
2 Tbsp. peanut oil (preferred) or any other oil
2 Tbsp. wine or cider vinegar
1 (4-7 lb) pork shoulder or fresh ham
Mix the first five ingredients together in a food processor, adding the oil in a drizzle and scraping the sides as necessary. Blend in the vinegar.
Rub this mixture well into the pork, getting into every nook and cranny you can find. Set meat on a rack and let sit, uncovered, for 1 to 24 hours. Refrigerate if time is greater than 2 hours.
Preheat oven to 350. Roast the pork for about 3 hours, turning every 30 minutes, until it is well done and very tender. Let sit for 10 to 15 minutes before cutting it up.