Cut small deep slit in each potato and bake in 375°F oven for about 1 hour or until tender. Meanwhile, peel rutabaga and cut into ½ inch cubes.
In pot of boiling salted water, cover and cook rutabaga for about 30 minutes or until very tender; drain well. Scrape out flesh from potatoes. In food processor or blender, combine sweet potato and rutabaga; puree, in batches, until smooth. Transfer to large bowl and set aside.
Peel, core and chop apples; sprinkle with lemon juice. In small saucepan, melt 2 tablespoons of the butter over medium heat; add apples, sugar, salt, pepper, cinnamon and nutmeg. Reduce heat to low and simmer, covered and stirring often, for 15 to 20 minutes or until apples are very tender. Transfer to food processor or blender and puree; stir into vegetable puree along with sour cream. Taste and adjust seasoning if necessary. Transfer to greased 6 cup casserole.
In small saucepan, melt remaining butter over low heat; cook almonds, stirring for 2 minutes. Sprinkle around edge of casserole; let cool to room temperature before covering and refrigerating for up to 3 days. To serve, bring to room temperature and reheat, uncovered, in 350°F oven for 30 to 40 minutes or until heated through. Makes 8 to 10 servings.