Notes: Mash boiled, steamed, or baked potatoes--hot or cold. If making ahead, cover and chill casserole up to 1 day; bake 55 minutes before adding nuts.
In a food processor or blender, smoothly purée spinach, parsley, garlic, oil, and lemon peel.
With a mixer, beat cream cheese until fluffy, adding 1 egg at a time. Add potatoes and mix well.
Spread potato mixture in a shallow 3- to 3 1/2-quart casserole. With the tip of a knife, impress shallow stripes or a lattice in potatoes, and spoon spinach mixture into these depressions.
Cover casserole tightly. Bake in a 375° oven until hot in center, about 35 minutes. Uncover and sprinkle nuts onto potatoes; bake 10 minutes more.
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