Yukon Gold-Stuffed Portobellos

Preheat oven to 450°.

Place potato in a saucepan; add water to cover. Bring to boil: cover, reduce heat, and simmer 20 minutes or until tender. Drain.

Remove brown gills from undersides of mushrooms using a sharp knife, if desired. Place mushroom caps on a jelly-roll pan, stem side down. Coat with cooking spray; sprinkle with 1/8 teaspoon each salt and pepper. Bake at 450° for 15 minutes, turning once.

Heat saucepan over medium heat until hot. Add butter and garlic; sauté 1 minute. Add milk, 3/4 teaspoon salt, and 1/4 teaspoon pepper; stir well. Return potato to saucepan; mash with a potato masher. Spoon 1 cup mashed potato onto each mushroom cap. Top each with

1 slice cheese; sprinkle with onions. Bake at 450° for 8 to 10 minutes or until cheese melts. Sprinkle with pepper. Serve immediately.