Prepare sous vide water bath to 72 C or 162 F. Combine the salt, five spice, and white pepper in a small bowl.
Insert the skewers through the pork belly slab, criss crossing in a X pattern. Score only the skin with a sharp knife. Season entire belly. Place in zip lock bag or vacuum seal bag and sous vide for 4-6 hours. Near end of sous vide cook time, turn broiler on high. Remove and pat the belly dry, especially the skin. Re-season and place on wire rack over roasting pan. Place on top rack underneat broiler and carefully monitor the crispening progess. Rotate if there are any spots getting darker than others. This process will take roughly 10-15 minutes. It's ok if there is some charring, excess charring can be scrapped off with knife. When skin bubbles up to turns golden brown remove from broiler and allow to cool for 10 minutes before slicing.
Calories: 4706kcal | Carbohydrates: 1g | Protein: 85g | Fat: 481g | Saturated Fat: 175g | Cholesterol: 653mg | Sodium: 4942mg | Potassium: 1696mg | Fiber: 1g | Sugar: 1g | Vitamin A: 94IU | Vitamin C: 3mg | Calcium: 58mg | Iron: 5mg