A tian is an earthenware vessel of Provence used both for cooking and serving. It is also the name of the dish prepared in it and baked in an oven. - Wikipedia

A lot of friends had asked for this recipe shortly after posting a picture of it on Facebook two weeks ago. The dish was born of the moment, inspired partly by too much pastis and perhaps a memory not quite my own. We had just gotten back from France, and my garden was overgrown with weeds competing for the same limited resources that nourished my vegetables. I was doing everything to avoid tackling the tangled mess, so I started reading Roger Verge's classic tome, 'Cuisine of the Sun' under the guise of research. I got to the pages where he delectably described in vivid detail a lunch with local fishermen in Cannes. They had just caught two beautiful John Dorys, and were preparing a large, festive tian for everyone to enjoy. Verge waxed on poetically about "potatoes gilded with saffron, ruddy tomatoes, pale onions, bluish thyme, green bayleaf and steel-grey fish" cooked in the local baker's oven and served in the golden May sunlight. I was hooked. Still deep within a pastis fueled cloud, I desperately wished I still was in Provence, playing petanque and living a simple, imaginary peasant life. The vision of Verge and his friends enjoying a hot tian straight out of the wood fired oven was much too much for me to bear, so armed with a pitchfork and shovel, I headed to my garden to dig for Yukon gold potatoes. I dug a heavy bucket load of creamy potatoes and a basket full of San Marzano tomatoes still warm from the sun. My hands were caked with dirt and sweat ran freely down my face when I returned to the kitchen muttering a bit incoherently. It was much like Richard Dreyfuss in the movie Close Encounters of the Third Kind when he built the mashed potato Devil's Tower to the horror of his family. All my wife Lisa got out of our one-sided conversation was to open a bottle of Corsican wine quickly because we were eating soon. Poor thing, still sleeps with at least one eye open and the weeds still cover our garden.

A casserole (French: diminutive of casse, from Provençal cassa "pan") is a large, deep dish used both in the oven and as a serving vessel. The word is also used for the food cooked and served in such a vessel, with the cookware itself called a casserole dish or casserole pan. - Wikipedia

Growing up I often thought of a tian solely as a layered vegetable dish, much like the one served by the rat chef in the popular children's movie Ratatouille, which technically was a tian more so than a ratatouille, because that is how my maman always made it. But tians can be made with anything - all vegetable, with meats, poultry, fish or anything else you want to cook and serve in it. I suppose casseroles are much the same, though whenever I hear the word casserole I want to start running. For me it conjures images of Campbell mushroom soup, crushed Saltines, frozen peas and canned tuna. Nowadays, I often compare Provencal tians to American casseroles; both are simple, homey dishes that enrich the soul and comfort when eaten. Interestingly, both words originate in Provence, and imply the same thing; the name applies both to the vessel and the dish you serve in it.This is a great way to celebrate the end of your summer vegetable garden, and the near end of the Alaskan halibut season in one easy dish that is incredible to eat.