Now is the time of year when root vegetables shine. For this hearty potpie, we roasted sweet, velvety rutabaga and carrots as well as a surprise addition, radishes, which livens the silky filling with their tempered bite. Strips of Napa cabbage melt into the middle, and for a simple flavor boost, store-bought vegetable broth is fortified with charred onions. The enticing topping: puff pastry. But you could choose the lid that fits your fancy: maybe cheddar biscuits, or even a layer of cornbread?