How to Make It
Preheat the oven to 400°F.
In a medium saucepan, bring the stock to a boil. Blanch the kale in the stock until tender, about 8 minutes. Transfer the kale to a 3-quart baking dish with a slotted spoon, pressing the liquid back into the saucepan with the stock. Boil the stock until reduced to 3 cups. Toss the chicken with the kale in the baking dish.
In a medium saucepan, heat 2 tablespoons of the oil over medium high heat until hot. Stir in 2 tablespoons of the garlic and the rosemary and cook, stirring until golden, about 4 minutes. Whisk in the flour and whisk, 1 minute. Whisk in the stock and bring to a boil, whisking. Boil the mixture until slightly thickened, about 10 minutes. Season with salt and pepper to taste, then pour over the chicken and kale in the baking dish.
Toss the breadcrumbs with the remaining 1 tablespoon each oil and garlic, then sprinkle evenly over the casserole.
Bake the casserole until the filling is bubbling and the crumbs are golden and crisp, 35 to 45 minutes.