How to Make It
Sprinkle pork evenly with salt. Place pork on a wire rack set inside a rimmed baking sheet. Chill, uncovered, 24 hours.
Preheat oven to 200°F. Melt butter in a large Dutch oven over low until sizzling. Add pork; cook, turning occasionally, until browned on 3 sides (do not brown side with bones), about 25 minutes. Remove from heat; pour off drippings from Dutch oven. Add wine, onions, and garlic to Dutch oven. Cover and transfer to preheated oven; bake 2 hours.
Remove pork from oven; uncover and add potatoes, stirring to coat. Increase oven temperature to 225°F. Cover and bake until a thermometer inserted in thickest portion of pork registers 195°F, 1 hour to 1 hour and 30 minutes. Remove from oven; let rest 20 minutes.
Transfer pork to a cutting board; remove and discard rib bone. Slice pork crosswise. Using a slotted spoon, lift potatoes, onions, and garlic from drippings, and divide among dinner plates. Top with pork belly, and serve.