Sweet Potato Souffle

Preheat oven to 400°F. Grease 2-quart soufflé dish with 1 tablespoon butter.

Place potato pieces in 3-quart saucepan; add water to cover. Bring to a boil over high heat. Reduce heat to medium-low; simmer, uncovered, 12 to 14 minutes or until pieces are fork-tender. (Do not overcook.) Drain. Transfer potatoes to large bowl; mash with potato masher until smooth. Stir in brown sugar, sherry, cinnamon and nutmeg until well blended; set aside.

Heat milk in small saucepan over medium heat until warm. Melt remaining 4 tablespoons butter in 2-quart saucepan over medium heat. Reduce heat to low; stir in flour. Cook and stir 2 minutes or until completely smooth. Gradually whisk in warm milk until well blended. Add salt; whisk constantly over medium heat 2 to 3 minutes or until sauce boils and thickens.

Whisk egg yolks into sauce mixture, one at a time, blending completely before adding next yolk. Cook and stir 1 minute more. Add to potato mixture; mix well. Set aside; cool completely.

Meanwhile, beat egg whites in large bowl with electric mixer at high speed until stiff peaks form. (After beaters are lifted, stiff peaks should remain; when bowl is tilted, egg whites should not slide.)

Using rubber spatula, stir 1/3 beaten egg whites into cooled potato mixture. Fold in another 1/3 egg whites by gently cutting down to bottom of bowl, scraping up side of bowl, then folding over top of mixture. Repeat until egg whites are incorporated into potato mixture. Fold in remaining egg whites.

Pour potato mixture into prepared dish, gently smoothing top. Place soufflé in center of oven; bake 10 minutes . Reduce oven temperature to 375°F. Bake 45 to 50 minutes more or until soufflé puffs up to rim of dish, center is set and top is lightly browned. Serve hot.