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1
Heat a medium pot over high heat for 2 minutes.
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2
Pour in 1/4 cup olive oil, and add the rosemary sprig and crumbled chile.
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3
Let them sizzle in the oil a minute.
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4
Add the diced onion, fennel, garlic, 1 tablespoon thyme, and the bay leaf, stirring a minute or two, until the onion is wilted.
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5
Add the flageolets, and cook a few more minutes, stirring to coat the beans with the oil.
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6
Cover with water by 3 inches, and bring to a boil over high heat.
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7
Turn the heat down to low, and place a paper towel over the beans to keep them under the surface.
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8
Simmer for 30 minutes, and then add 2 1/2 teaspoons salt to the beans.
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9
Continue cooking on a low simmer about 1 hour, until the beans are tender.
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10
As the beans cook, add water as necessary (but dont add too muchyou want these juices to be rich and a little starchy, since they will be an important part of the finished gratin).
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11
Remove the beans from the heat, and let them cool in their juices.
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12
Taste for seasoning.
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13
While the beans cook, caramelize the sliced onions.
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14
Heat a large saute pan or Dutch oven over high heat for a minute.
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15
Swirl in the remaining 3 tablespoons olive-oil, and add the sliced onions, 2 teaspoons thyme, 1 teaspoon salt, and some freshly ground black pepper.
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16
Cook 6 minutes, stirring often.
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17
Turn the heat down to medium, and stir in 1 tablespoon butter.
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18
Cook 15 minutes, stirring often and scraping with a wooden spoon, until the onions start to caramelize.
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19
Turn the heat down to low, and continue to cook about 10 minutes, stirring often, until the onions are a deep golden brown.
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20
Spread the onions on the bottom of a 9-by-9-inch (or equivalent) gratin dish.
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21
Spoon the flageolets into the gratin dish with a good amount of their cooking juices.
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22
The beans will expand a little as they bake, so fill the gratin dish only three-quarters full (reserve any extra beans for use in another dish).
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23
Preheat the oven to 425F.
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24
Toss the breadcrumbs in a medium bowl with the remaining teaspoon thyme and the chopped parsley.
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25
Melt the remaining 4 tablespoons butter in a small saucepan over medium heat.
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26
Cook about 3 minutes, swirling the pan occasionally, until the butter browns and smells nutty.
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27
Pour the brown butter over the breadcrumbs (make sure to scrape up all the brown bits), let cool a minute or two, and toss to combine.
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28
Sprinkle the brown butter breadcrumbs over the beans, and bake 1 1/2 hours, until the gratin is bubbling, nicely browned, and crispy on top.
