1tablespoonminced fresh rosemary or 1 teaspoon crumbled dried rosemary
3tablespoonsunsalted butter
½cupall-purpose flour
4cupscubed or shredded cooked chicken
½cupheavy (whipping) cream or half-and-half
½cupchopped fresh flat-leaf parsley
2large Idaho (all-purpose) potatoes (about ¾ pound), peeled and grated (see Note)
Instructions
Preheat the oven to 375°F.
Heat 1 tablespoon of the olive oil in a very large skillet, Dutch oven, or wok over medium-high heat. Add the garlic, onions, potatoes, carrots, and celery and sauté to soften for 4 minutes. Add the broccoli, season with salt and pepper, and sauté until the vegetables are coated with the onion mixture, 1 minute. Add ½ cup of the broth, stir, and cover. Simmer until all of the vegetables are just crisp-tender and the liquid is mostly evaporated, about 3 minutes. Stir in the peas and the corn. Transfer the entire mixture to a 13x9 inch pan. Return the skillet to the stove.
Heat another 1 tablespoon olive oil in the pan over medium-high heat. Add the mushrooms and rosemary and sauté until the mushrooms are golden brown, 5 minutes. Add them to the vegetable mixture and return the pan to the stove.
Melt the butter in the pan over medium heat. Whisk in the flour and whisk occasionally until it turns blond in color, about 3 minutes. Add the remaining 3 1/2 cups broth and bring to a simmer over high heat. Lower the heat back to medium and simmer, whisking occasionally, until the sauce has thickened, about 3 minutes. Season with salt and pepper, stir in the chicken, cream and parsley, and cook for 3 minutes more. Pour the sauce over the vegetable mixture and stir so that everything is well combined.
Place the shredded potatoes in a clean dish towel and twist and squeeze over the sink to remove as much water as possible from the potatoes. In a medium sized bowl toss the shredded potatoes with the remaining tablespoon of oil, and season with salt and pepper. Evenly distribute the potatoes over the casserole.
Bake for 30 minutes until the potatoes are tender and golden brown browned on top. Serve hot. Spoon the casserole onto plates, making sure each serving has some of the potato topping.
Notes
If you prefer to use frozen hash browns instead of shredding your own potatoes that is a great shortcut.