ATK Cannellini Bean Gratin

America's Test Kitchen Cannellini Bean Gratin

3 tablespoons olive oil
3 onions, halved and sliced thin through root end
1/2 tsp brown sugar
6 garlic cloves
1/8 tsp red pepper flakes
1/2 cup dry white whine
4 15-ounce cans chickpeas
1 cup vegetable broth
1 tsp minced fresh rosemary or 1/4 tsp dried
2 ounces Parmesan cheese, grated (1 cup)
Salt and pepper
4 ounces Gruyere cheese, shredded (1 cup)
2 tablespoons minced fresh parsley

1. Adjust oven rack to middle position and heat oven to 375 degrees. Heat 2 tablespoons oil in Dutch oven over medium-high heat until shimmering. Add onions and sugar and cook, stirring frequently, until softened, about 5 minutes. Reduce heat to medium-low and continue to cook, stirring often, until onions are dark golden and caramelized, 20 to 25 minutes.

2. Stir in garlic and pepper flakes and cook until fragrant, about 30 seconds. Stir in wine and cook until nearly evaporated, about 1 minute. Transfer onion mixture to 13 by 9 inch baking dish and spread into even layer.

3. Add beans, broth, and rosemary to now empty pot and bring to brief simmer, about 1 minute. Off heat, gently stir in remaining 1 tablespoon oil and Parmesan. Season with salt and pepper ot taste, spread evenly over onions, then sprinkle with Gruyere.

4. Bake, uncovered, until cheese is lightly golden and bubbling around edges, 15 to 20 minutes. Sprinkle with parsley and serve.