How to Make It
Preheat oven to 200°F.
Using a mandoline, slice sweet potatoes into 1/8-inch-thick slices. Place in a large bowl; add 2 teaspoons oil, and toss to coat.
Place sweet potato slices in a single layer on 2 baking sheets lined with parchment paper; sprinkle evenly with 1/2 teaspoon salt. Bake at 200°F for 1 hour and 30 minutes. Increase oven temperature to 400°F; bake for 10 minutes. Remove from oven; cool completely.
Meanwhile, heat remaining 1 tablespoon oil in a large nonstick skillet over medium-high. Add onion; sauté 8 to 10 minutes or until tender. Reduce heat to medium-low. Stir in shallots, thyme, pepper, and remaining 1 teaspoon salt; cook, stirring occasionally, 40 minutes or until golden brown.
Increase heat to medium. Add garlic and Worcestershire sauce; cook, stirring occasionally, 5 minutes. Remove pan from heat, and let cool 15 minutes.
Place tofu, yogurt, and juice in a blender; process until smooth. Stir together onion mixture and yogurt mixture in a bowl. Top with chives. Serve with sweet potato chips.