Clean the ribs and trim away excess fat. Prepare a spice mix by combining sugar, 1/4 cup salt, ground black pepper, paprika, 1 teaspoon cayenne pepper, and garlic powder. Coat the ribs liberally with the spice mix and place them in roasting pans. Cover and refrigerate for at least 8 hours.

Preheat oven to 275°F (135°C). Bake the ribs uncovered for 3-4 hours, or until they are tender and nearly falling apart.

Remove 5 tablespoons of drippings from the pans and heat them in a skillet over medium heat. Cook onion in the drippings until browned and tender. Stir in ketchup and heat for 3-4 more minutes, stirring constantly. Add water and brown sugar, then season with cayenne, salt, and pepper. Simmer for 1 hour on low heat, adding water as needed to maintain desired thickness.

Preheat the grill for medium-low heat.