In a large saucepan over high heat, boil potatoes 15 to 20 minutes or until tender; drain and set aside.
In a medium saucepan over medium heat, sauté onions in butter for 3 to 5 minutes or until translucent. Stir in sugar, salt and flour. Gradually add milk, stirring after each addition.
Reduce heat to low and simmer until thick, stirring constantly. Stir in sour cream, vinegar and TABASCO® Sauce; simmer until bubbly. Add potatoes to sauce and serve immediately.
Makes 4 to 6 servings.