Preheat oven to 375°F (190°C). Heat oil in a large skillet over medium heat. Add onion and salt; cook5 minutes or until softened. Add sweet potato and garlic; heat just until sweet potato is tender, about 2 minutes.
Whisk together eggs, milk, cheese, thyme and black pepper in a large bowl. Stir in cooked vegetables. Divide among 8 standard-sized greased muffin cups. Bake until frittatas are set, about 20 minutes. Let cool for a couple of minutes before unmoulding.
Meanwhile, place sour cream, roasted red pepper, lemon juice, paprika and salt in a blender or food processor. Blend until smooth.
Serve frittatas with pepper sauce.
Nutrients per serving: 353 calories, 21 g protein, 21 g fat (10 g saturated fat), 14 g carbohydrates (6 g sugars), 1 g fibre, 453 mg cholesterol, 784 mg sodium.