Preheat the oven to 150 C (300 F). Pat the ribs dry with paper towels so the rub sticks and the surface can brown properly.
Mix brown sugar, smoked paprika, salt, pepper, and garlic powder. Rub the mixture all over the ribs, pressing it into the meat so the flavors penetrate the surface.
Place ribs bone-side down on a foil-lined tray and cover tightly with foil. Roast for 2 to 2.5 hours until the meat is tender and you can pull the meat slightly from the bone with a fork.
While ribs roast, cut the potatoes into 1 cm (1/2 inch) sticks. Soak in cold water for 30 minutes to remove excess starch for crisp fries.
Drain and dry the potatoes thoroughly. Toss with vegetable oil and a pinch of salt. Spread in a single layer on a baking sheet and bake at 220 C (425 F) for 20-30 minutes, flipping halfway, until deep golden and crisp.
When ribs are tender, increase oven to 230 C (450 F). Brush a generous layer of BBQ sauce over the ribs and return uncovered for 8-12 minutes until the sauce is sticky and caramelized - watch closely to avoid burning.
Rest ribs loosely tented for 5 minutes to let juices redistribute. The aroma should be sweet, smoky, and slightly charred at the edges, while the texture pulls apart easily without collapsing into mush.
Serve ribs with fries hot from the oven. For extra zing, offer a vinegar-based slaw or pickles to cut the richness and add crunch.