Dice and chop all your ingredients. Then, preheat oven to 300
Place the focaccia pieces spread out evenly on a baking sheet. Bake for about 10 to 15 minutes to stiffen them up. They don't need to be croutons. But, you don't want them soft, otherwise, they will fall apart when you add the stock, and you'll get mush. If you can, it helps to leave them out for a day or two before cooking, so they are already a bit stale.
Heat a layer of oil in a wide pot. Saute the vegetables over medium high heat until translucent. Then, melt in the butter and add the broth. Bring to a simmer. Fold in all the remaining ingredients and mix well. Transfer to a sprayed baking pan. Spread out evenly. Place pan in the preheated oven and allow to bake at least 30 minutes. The top should get lightly brown and crusty. Check the temperature by using a meat thermometer. You want the center to be at 165 degrees. If you want it crisper, give it a little more time. You could also top with a couple pats of butter for an extra buttery flavor.
Serve hot as is, or allow to cool and cut portions to reheat as needed.