I use this terrific, nourishing soup as a filling weeknight supper. Use any combination of onions you like, making it great all year long: yellow onions, red onions, leeks, shallots, cipolline, even green onions. And when it is cold outside, I caramelize the onions longer for deeper flavor.
In 12- to 14-inch skillet, heat oil over medium-high heat. Add garlic; cook and stir until garlic begins to brown. Stir in onions and salt. Cook about 7 minutes. Reduce heat to medium. Cook about 10 minutes longer, stirring occasionally, until onions are golden brown.
Stir in sage and vinegar. Cook 2 to 4 minutes, stirring occasionally, until liquid has evaporated. Stir in broth. Simmer over medium heat 10 minutes, stirring occasionally.
Meanwhile, set oven control to broil. Sprinkle bread with cheese; place on cookie sheet. Broil with tops 4 to 6 inches from heat until cheese is melted (watch carefully). Place 1 slice of bread on each serving of soup.
Per Serving: 349 calories; protein 13.8g; carbohydrates 44.9g; fat 12.8g; cholesterol 18.1mg; sodium 1317.3mg.