For the cassoulet: Combine the dried beans, 1 tablespoon salt and 8 cups hot water in a medium saucepan over high heat. Bring to a boil and cook for 2 minutes, then remove from heat and cover with a lid. Let sit for 1 hour, until the beans are "al dente" (softened but still with some bite). Drain the beans and rinse under cold water.
Preheat the oven to 375 degrees F.
In a large Dutch oven over medium-low heat, add 1 tablespoon extra-virgin olive oil. When the oil is hot, add the bacon lardons. Slowly render the fat out of the bacon and cook until crispy, stirring occasionally, about 15 minutes. Drain the bacon on a paper towel-lined baking sheet.
Increase the heat to medium and add the sausages to the rendered bacon fat. Brown on both sides, 4 to 5 minutes per side. Drain on the baking sheet.
Season the chicken thighs and drumsticks generously on both sides with salt and pepper. In two batches, add the chicken to the Dutch oven and cook until deep golden brown, about 5 minutes per side. Drain on the baking sheet.
Stir the onions, carrots, fennel and celery into the rendered fat; sprinkle with salt and pepper. Cook until softened, about 8 minutes. Stir in the garlic and cook until softened, 2 minutes. Add the tomato paste; cook for another 2 minutes, until evenly combined with the vegetables and just beginning to toast. Add the diced tomatoes, chicken stock, white beans, parsley, rosemary and thyme. Bring the mixture to a boil, then lower the heat to a simmer.
Cut the sausages on the bias into thin rounds and add them to the pot along with the bacon, stirring to combine. Transfer the cassoulet to a 9-by-13-inch baking dish. Top with the chicken thighs and drumsticks; drizzle 1 tablespoon olive oil over the chicken.
Place the baking dish on a baking sheet and transfer to the oven. Bake until the top of the cassoulet turns a rich, deep brown color, the liquid has reduced and the beans have risen to the surface, about 1 hour 30 minutes.
Remove from the oven and let rest for 10 minutes.
For the breadcrumb topping: Meanwhile, melt the butter in a large sauté pan over medium-high heat. When the butter has melted, add the breadcrumbs and 1/2 teaspoon salt. Toast the breadcrumbs until golden brown, stirring often, 3 to 4 minutes. Remove from the heat and stir in the lemon zest and parsley.
To serve: Garnish the cassoulet with the breadcrumb topping and some fennel fronds. Serve immediately!