When its baked to within an inch of its life. You can't lose with something that is as easy to make as a sandwich, is greater than the sum of its parts, and with all the unctuousness of a dish that took far longer to put together. Winner.
Not exactly a recipe here, more a few suggestions for what I did. Basically layers of bread, pesto, cheese and a fig leaf of vegetable matter. The pesto adds a flavour boost, the bread provides the structure, the cheese gives it some ooze, and the vegetables are the redeeming element. This all got layered up as so...
The carrots were the weakest links being a little too hardy to get soft enough in the cooking time. This would be the perfect opportunity to use up leftover roasted veg. I'm also not going to pretend that this is the time to go easy on the cheese.
Et voila. The next bit was the savoury custard mix. I used about four eggs whisked with an equal volume of milk and seasoned. This was whacked on top and the whole lot refrigerated until cooking time. Then 30 minutes in the oven and a bit of grilling time to make the top extra crispy.
And if you serve it with kale, it has no calories. Fact.