Agreed, great book. There is a second book in that series, The Boy On the Bridge, I believe. Also quite good.
I found the movie on Kanopy through my (Canadian) public library. I’m not sure how easy to find it is on other services, as it’s not exactly blockbuster stuff. I discovered it quite by accident.
I expect it’s to generate steam in the oven for the first part of the bake. I just put ice chips in my Dutch oven after I get the boule in there, but I should try this.
Steam contributes to a good rise, if I’m not mistaken.