Tomato Gratin with Bacon

A good tomato gratin is a little like a pizza without the crust. The trick is to use the largest baking dish or roasting pan you have, so you can spread the tomato slices in a single layer. You can make the simplest version with a little Parmigiano-Reggiano and olive oil, or you can be a little more extravagant and use cream, instead of the oil, and bacon along with the cheese. However you approach this gratin, the point is the same: you want the tomatoes to release their liquid and then th