Prepare the Tomato-Curry Sauce

1. Heat oil in a medium saucepan over medium. Add onion; cook, stirring often, until softened and starting to caramelize, about 8 minutes, reducing heat, as needed, to prevent burning. Add tomato paste, curry powder, and paprika; cook, stirring constantly, for 1 minute. Add brown sugar, tamari, salt, garlic, crushed tomatoes, and cinnamon stick; bring to a boil over medium-high. Reduce heat to medium-low; cook, stirring occasionally, until slightly thickened, about 10 minutes. Remove and discard cinnamon stick; add vinegar. Remove saucepan from heat; process mixture using an immersion blender until smooth, 30 seconds. Stir in water. Place saucepan over medium-low heat, and cook, stirring occasionally, until warmed through, about 1 minute. (Sauce will be smooth and spreadable, similar to ketchup consistency.) Keep warm.

Prepare the Currywurst

1. Place 2 baking sheets on middle rack in oven; preheat oven to 450°F. Heat 1 tablespoon of the oil in a large skillet over medium-high. Add bratwursts, and cook until browned on all sides and an instant-read thermometer inserted into center of bratwursts registers 155°F, about 10 minutes. Remove skillet from heat; add curry powder to bratwursts, and toss until sausages are evenly coated. Transfer bratwursts to a cutting board; let rest for 5 minutes.

2. Meanwhile, place frozen fries in a large bowl; add remaining 3 tablespoons oil, and toss to coat. Carefully pour fries evenly onto preheated baking sheets, and bake in preheated oven for 8 minutes. With baking sheet still in the oven, increase oven temperature to broil; cook, stirring occasionally, until very crispy and golden brown, 6 to 8 minutes. Remove from oven, and sprinkle evenly with salt; toss to coat.

3. Slice bratwursts on an angle into 1-inch pieces; spoon over Tomato-Curry Sauce. Serve with fries.