Mashed Potato, Rutabaga and Parsnip Casserole with Caramelized Onions

Preparation

1. Step 1

   Butter 13 x 9x2-inch glass baking dish. Combine first 7 ingredients in large pot; bring to boil. Reduce heat, cover partially and simmer until vegetables are very tender, about 30 minutes. Drain well. Transfer vegetables to large bowl. Add 1/2 cup butter. Using electric mixer, beat mixture until mashed but still chunky. Season with salt and pepper. Transfer mashed vegetables to prepared dish.

   Step 2

   Melt remaining 1/4 cup butter in heavy large skillet over medium-high heat. Add sliced onions and sauté until beginning to brown, about 5 minutes. Reduce heat to medium-low and sauté until onions are tender and golden brown, about 15 minutes. Season with salt and pepper. Spread onions evenly over mashed vegetables. (Casserole can be prepared up to 1 day ahead. Cover and refrigerate.)

   Step 3

   Preheat oven to 375° F. Bake casserole uncovered until heated through and top begins to crisp, about 25 minutes.