Heat oven to 350°F. Pierce sweet potatoes all over with fork; place on cookie sheet with sides. Bake about 1 hour 15 minutes or until tender when pierced with fork. Let stand 15 minutes or until cool enough to handle.
Meanwhile, in 10-inch skillet, cook bacon over medium-high heat 4 minutes, turning occasionally, until brown. Remove bacon from skillet; place on paper towels to drain. Reserve 1 tablespoon drippings in skillet; discard remaining drippings. Add onion to skillet; cook over medium heat 5 to 8 minutes, stirring occasionally, until softened.
Peel sweet potatoes; place in large bowl. Mash until no lumps remain. Add warm half-and-half, thyme, salt and pepper; mash until very smooth.
Add onion to sweet potatoes. Crumble bacon; reserve 2 tablespoons for garnish. Add remaining bacon to potatoes; stir until blended. Garnish with reserved bacon and thyme sprigs.