To make filling: In a large skillet, heat olive oil over medium heat. Add onion and sauté until translucent, about 3-4 minutes. Add garlic and ginger and sauté for another minute until fragrant. Carefully add a tablespoon or so of water to loosen the spices and create a paste. Stir in curry powder, cumin, coriander, turmeric and cayenne pepper (if using). Cook for 1-2 minutes until the spices are well-toasted and aromatic.

Add the grated sweet potatoes and carrots. Cook, stirring occasionally, until the vegetables are tender, about 5-7 minutes. Lightly season with salt and pepper. Remove from heat and let the mixture cool slightly. Taste the mixture and add more salt and pepper if needed.

To assemble the spring rolls: Take one spring roll wrapper and dip it into warm water (if your papers provide different instructions, use those). Place the paper on a clean surface with one corner pointing towards you. Place about 2-3 tablespoons of the sweet potato filling near the bottom corner of the wrapper.

Fold the bottom corner over the filling, then fold in the sides, and roll up tightly. Brush the top corner with the cornstarch mixture to seal the roll. Repeat with the remaining wrappers and filling. Place them several inches apart from each other to prevent sticking.

To cook spring rolls: Heat oil in a large frying pan or deep fryer to 350°. Fry the spring rolls in batches, turning occasionally, until they are golden brown and crispy, about 3-4 minutes per batch. Remove from the oil and drain on a paper towel-lined plate.

To make dipping sauce: Combine all ingredients in a small bowl and mix well.