Heat oil in stockpot over medium heat until hot. Place beef pot roast in stockpot; brown evenly. Remove pot roast; pour off drippings and season with 1 teaspoon salt and 1/2 teaspoon pepper.
Add onion and thyme to stockpot; cook and stir 3 to 5 minutes or until onion is tender. Add broth and cider; increase heat to medium-high. Cook and stir 1 to 2 minutes or until browned bits attached to stockpot are dissolved. Return pot roast to stockpot; bring to a boil. Reduce heat; cover tightly and simmer 2-1/2 hours.
Add sweet potatoes and garlic to stockpot; continue simmering, covered, 30 minutes or until sweet potatoes and pot roast are fork-tender.
Remove pot roast; keep warm. Remove sweet potatoes and garlic with slotted spoon to large bowl, leaving cooking liquid in stockpot.
Add maple syrup, ginger, remaining 3/4 teaspoon salt and 1/4 teaspoon pepper to sweet potatoes. Beat until sweet potatoes and garlic are mashed and smooth; keep warm.
Skim fat from cooking liquid; stir in cornstarch mixture. Bring to a boil, stirring constantly; cook and stir 1 minute or until thickened.
Carve pot roast into slices; serve with mashed sweet potatoes and gravy.