Pat the ribs dry and remove any silver skin. Set aside in a roasting pan that holds them more or less in a single layer—some overlap is okay, but you don't want them stacked on each other.
Heat a small frying pan over medium-high heat. Add the Sichuan peppercorns and cook until fragrant and toasted, about 2 minutes. Transfer to a mortar, let cool a few minutes, and then grind with the pestle (you can also grind them in a spice grinder or crush them with the bottom of a heavy pan).
In a small bowl, combine the ground Sichuan peppercorns, sugar, salt, smoked paprika, cayenne, black pepper, and cumin.
Rub the spice mix evenly all over the ribs. Cover the dish with foil and chill at least overnight and up to 2 days.
Preheat an oven to 300°F. Bake the ribs, still covered, for 3 hours.
Remove the pan from the oven and uncover the ribs. They should be completely tender. If they aren't, return, covered, to the oven and cook until they are, testing every 30 minutes. If the are fork tender... depending on the ribs, you may have a lot of liquid in the pan (industrially raised pork tends to let off a lot of water). If it's more than a few tablespoons, drain off but reserve the liquid. Baste the ribs with their liquid, and return, uncovered, to the oven. Increase the oven temperature to 425°F. Bake the ribs another 30 minutes, basting them every 10 minutes. Let rest 15 minutes before cutting apart and serving.