Pour the dried beans into a bowl. Cover with cold tap water and soak overnight.
The next morning, brush mustard all over the ribs. Mix brown sugar and barbeque seasoning and rub on both sides of ribs. Leave out of the refrigerator for one hour before cooking.
Add bacon grease to a Dutch oven heated on medium high heat. Brown the ribs on all sides, working in batches. When browned, remove and set aside.
In same skillet, add onions, carrots and celery. Cook for 10 to 15 minutes, stirring occassionally, or until the volume has reduced by half.
Add garlic, sage, salt and pepper. Continue cooking for 5 minutes, stirring occasionally.
Drain beans and add to pot.
Add chicken stock and diced tomatoes. Stir.
Placed browned ribs on top of bean mixture. Place thyme twigs in pot.
Cover and cook at 300 degrees for 3 hours.
After 3 hours, increase heat to 325 degrees and uncover. Cook for an additional hour or until the liquid cooks down to the level of the beans.
Taste for seasonings and adjust before serving.