Heat 1 teaspoon oil in a large Dutch oven over medium-high heat. Add onion; sauté 10 minutes or until tender and golden brown. Add garlic; sauté 1 minute. Spoon onion mixture into a large bowl.
Place flour in a shallow bowl or pie plate. Dredge beef in flour, shaking off excess. Heat remaining 2 teaspoons oil in pan over medium-high heat. Add half of beef mixture; sprinkle with 1/4 teaspoon salt. Cook 6 minutes, browning on all sides. Add browned beef to onion mixture. Repeat procedure with remaining beef mixture and 1/4 teaspoon salt.
Add wine to pan, scraping pan to loosen browned bits. Bring to a boil; reduce heat, and simmer 10 minutes or until liquid is reduced to about 1 cup. Add beef mixture, broth, thyme, and vanilla bean half, if desired. Bring mixture to a simmer. Stir in remaining 1/2 teaspoon salt and pepper. Cover, reduce heat to medium-low, and simmer 1 hour or until beef is just tender.
Discard thyme sprigs and vanilla bean half. Stir in celeriac and dried plums. Simmer, uncovered, 1 hour or until beef and vegetables are very tender and sauce is thick, stirring occasionally.