How to Make It
Stir together salt, sugar, garlic, shallots, anise, lime zest, orange zest, mustard seeds, fennel seeds, and pepper in a medium bowl. Sprinkle ribs liberally with salt mixture, pressing to adhere. Cover and chill 8 hours or overnight.
Preheat oven to 225°F. Uncover ribs, and remove as much of the salt mixture as possible. Place 1 rack of ribs on a 5-foot-long piece of plastic wrap; roll ribs in plastic wrap until tightly sealed, at least 15 times. Repeat with second rack of ribs.
Place wrapped short ribs on a rimmed baking sheet or roasting pan. Bake in preheated oven until meat feels tender to the bone, about 5 hours. Chill until plastic sets and is cool enough to handle.
Cut off and discard plastic wrap, and remove ribs. Increase oven temperature to 400°F. Return ribs to baking sheet, and top with butter, garlic, and thyme. Bake at 400°F until ribs are heated through and browned, 7 to 10 minutes, basting occasionally with melted butter mixture.