Preheat oven to 300°.
Heat oil in a large Dutch oven over medium-high heat. Add beef to pan, browning on all sides (about 8 minutes). Remove from pan. Coat pan with cooking spray. Add onion to pan; sauté 5 minutes or until beginning to brown. Stir in broth, scraping pan to loosen browned bits. Reduce heat; add mustard and next 5 ingredients (through bay leaves). Return roast to pan; bring to a simmer.
Cover and bake at 300° for 1 1/2 hours. Stir in rutabaga, parsnip, and carrot. Bake, covered, 1 hour. Stir in potato; cover and bake 30 minutes or until roast and vegetables are very tender. Discard bay leaves. Garnish with thyme sprigs, if desired.