Bring a large pot of water to a rolling boil, add a generous amount of salt and add kale. Blanch for 2 to 3 minutes, Remove from the water and transfer to a bowl of cold water. Drain and squeeze hard to expel excess water. Chop medium-fine or cut into thin ribbons.
Heat 2 tablespoons of the oil over medium heat in a large, heavy skillet and add onion. Cook, stirring often, until tender, about 5 minutes, and add fennel. Cook, stirring often, until the fennel begins to soften. Add salt to taste and continue to cook, stirring often, until the fennel is very tender and fragrant, about 8 minutes. Add garlic and kale, stir together for another minute, then stir in dill. Season to taste with salt and pepper, and remove from the heat.
Preheat oven to 375 degrees. Oil a 2-quart gratin or baking dish. Beat eggs in a large bowl. Whisk in milk and salt to taste (I use about 1/2 teaspoon). Stir in fennel and kale mixture, rice and Gruyère, and combine well. Taste and adjust seasonings. Scrape into baking dish. Sprinkle breadcrumbs over the top if using, and drizzle on the remaining tablespoon of oil. Bake 35 to 40 minutes, until set and the top and sides are beginning to color. Remove from oven and allow to sit for at least 10 minutes before serving. This is good hot, warm, or room temperature.