Roast like a pro: First, plan ahead. A bone-in roast this thick requires two days of seasoning to allow the salt to penetrate to the bone. (That's as many days as ingredients required to flavor this budget-minded wonder.) Second, score the skin using a box cutter or razor blade so the fat renders as it cooks and the exterior turns potato chip crunchy.
The right temp: Because we're talking shoulder, go for an internal temp of at least 175°, which will encourage the connective tissue to break down and intramuscular fat to melt.
1. Make 1/4-inch-deep cuts 1/4 inch apart in skin of ham with a clean box cutter. (The sharp blades cut through the skin with ease and make straight edges.) Stir together salt and pepper; rub over ham, working into cuts in skin. Place ham in a very large bowl, and cover with plastic wrap. Chill 2 days.
2. Remove ham from bowl. Brush salt from ham, and discard. Place ham, fat side up, on a wire rack in a jelly-roll pan, and chill, uncovered, 8 to 10 hours to air-dry.
3. Let ham stand at room temperature 1 hour.
4. Preheat oven to 425°. Bake ham on lower oven rack 45 minutes. Reduce oven temperature to 325°, and bake 2 hours and 30 minutes. Increase oven temperature to 425°, and bake 30 to 35 minutes or until skin is crisp and a meat thermometer inserted into thickest portion registers 175°. Let stand 30 minutes before slicing. Serve with salsa.