Traditionally a shepherd’s pie contains leftover roasted lamb–an easy way to use leftovers in a comforting one-dish recipe. This version is updated using fresh chicken and topped with mashed golden potatoes and cauliflower—a modern nod to upping the veggie ante in a rustic home style recipe.
Heat oven to 400˚F. Oil a 2-quart casserole or baking dish.
Heat 1 tablespoon oil in a large skillet over medium-high heat; sauté chicken and garlic about 5 minutes; remove to a plate. Add remaining 1 tablespoon oil to skillet; add onion, rutabaga, carrots and mushrooms; season with salt and pepper. Cook and stir about 8 minutes or until softened.
Stir cornstarch into chicken broth until dissolved; pour into skillet and heat bring mixture to a boil, stirring frequently. Remove from heat. Stir in chicken, peas, and half of herbs. Spoon into prepared casserole dish.
Meanwhile, fill a large saucepan with water and bring to a boil. Cook potatoes and cauliflower for about 10 minutes or until tender. Drain well.
Place potatoes and cauliflower in a large bowl. Mash until just smooth; stir in egg and remaining herbs. Season well with salt and pepper.
Spoon potato-cauliflower mixture over the top of the chicken filling in the baking dish. Spread to entirely cover the top, swirling with the back of a spoon.
Bake casserole 25 to 30 minutes or until top is golden brown and crisp.