Preheat oven to 375°F (190°C). Cut a small, deep slit in each sweet potato.

Bake sweet potatoes for about 1 hour or until tender.

Peel the rutabaga and cut into 1/2 inch cubes.

In a pot of boiling salted water, cook rutabaga for about 30 minutes or until very tender. Drain well.

Scrape out the flesh from the baked sweet potatoes.

In a food processor or blender, combine sweet potato and rutabaga. Puree in batches until smooth. Transfer to a large bowl and set aside.

Peel, core, and chop apples. Sprinkle with lemon juice.

In a small saucepan, melt 2 tablespoons of butter over medium heat. Add apples, brown 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 the apple mixture to a food processor or blender and puree.

Stir the apple puree into the vegetable puree along with sour cream. Taste and adjust seasoning if necessary.

Transfer the mixture to a greased 6-cup casserole dish.

In a small saucepan, melt the remaining butter over low heat. Cook the sliced almonds, stirring for 2 minutes.

Sprinkle the almonds around the edge of the casserole dish.

Let the casserole cool to room temperature before covering and refrigerating for up to 3 days.

To serve, bring to room temperature and reheat, uncovered, in a 350°F (175°C) oven for 30 to 40 minutes or until heated through.