Instructions: 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.

Melt remaining 1/4 cup butter in heavy large skillet over medium-high heat.

Add sliced onions and saute until beginning to brown, about 5 minutes.

Reduce heat to medium-low and saute 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.)

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

Serves 8 to 10.

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