1. Heat oil in a small saucepan over medium-high heat. When oil shimmers, add onions and salt and cook, stirring occasionally, until soft and golden brown in places, 8-10 minutes. Add garlic and continue cooking, 1 minute more. Stir in tomato paste, red wine vinegar, hot sauce, sugar, and 1/2 cup water. Bring to a boil, reduce heat, and simmer, stirring occasionally, until onion relish is thick and glossy.

2. Bring 1 inch of water to a boil in a deep-sided skillet. Add hot dogs, reduce heat, keeping water at a bare simmer, and heat through at least 10 minutes, or until ready to serve.

3. Line a steamer basket with three layers of cheesecloth and place inside a pot with 1/2 inch of boiling water. Place hot dog buns on cheesecloth, cover pot, and steam buns, 2 minutes.

4. Assemble: Place hot dogs inside buns, top with onion relish, spicy brown mustard, and sauerkraut and serve immediately.