For the filling:
3 Tbsp olive oil
3 leeks, quartered lengthwise, thinly sliced crosswise
4 garlic cloves, minced
1 lb butternut squash, peeled and cut in to 1/2 inch cubes
1 can Cannellini beans, drained
1 bunch Lacinato kale, chopped
3 cups stock (veggie or chicken)
1 rosemary sprig
3/4 cup finely grated Parmesan cheese
Coarse salt and freshly ground pepper
For the topping
2 cups flour
2 tsp baking powder
1 stick cold unsalted butter, cut into small pieces
1 cup finely grated Parmesan cheese
1/1/3 cups heavy cream, plus more for brushing
1 Make the filling: Heat oil in a large cassoulet over medium heat. Cook leeks and garlic until tender, about 5 minutes. Add butternut squash, beans, kale, stock, rosemary. Bring to a gentle simmer. Cook covered until vegetabes are just tender, about 20 minutes. Stir in cheese, and season with salt and pepper. Let cool.
2. Preheat oven to 375. Make the topping: Whisk together flour, baking powder, and 1 tsp salt in a medium bowl. Cut in butter using a pastry cutter or rub in with your fingers until small clumps form. Stir in cheese. Add cream, and stir with a fork until a sticky dough forms. Divide into 8 balls (about 1/2 cup each).
3. Transfer filling to an 11 by 13 inch (10 cup) baking dish. Top with dough balls, and brush with cream. Bake until topping is golden and filling is bubbling, about 55 minutes. If biscuits darken too quickly, cover with foil.