Pork Rib Ragu

Preheat oven to 350 degrees. Halve leek lengthwise and rinse thoroughly; dry well and coarsely chop. In a large Dutch oven or heavy pot, heat oil over medium-high. Season ribs with salt and pepper. In batches, cook ribs until browned, 4 to 6 minutes per batch. Transfer ribs to a plate. Add leek, carrots, and celery to pot. Cook, stirring frequently, until vegetables soften slightly, about 5 minutes. Add wine; bring to a simmer and reduce wine by half.

Return ribs to pot and cover with water by 2 inches. Bring to a boil, cover, then place pot in oven. Cook until meat is falling off bones, about 3 1/2 hours. Transfer ribs to a rimmed baking sheet and strain cooking liquid into a heatproof container; skim fat from liquid. When ribs are cool enough to handle, shred meat (discard fat and bones).

In a medium saucepan, melt butter over medium. Add onion and cook until soft, about 8 minutes. Stir in flour to coat. Gradually whisk in cooking liquid and simmer until thickened, about 8 minutes. Add pork to sauce and heat through.