When the spoon bread first comes out of the oven, it will be lovely and puffed. It will settle fairly quickly, and that’s ok — it’s not meant to be served like a soufflé, where time is of the essence. If you can get it to the table straight from the oven when it is at its most majestic, great! But really, by the time you serve it up it will have settled into its delicious self anyway. And yes, serve it hot, but second helpings at room temperature are delicious.