Cornflake, Pecan, and Marshmallow-Topped Sweet Potato Casserole

INGREDIENTS

• 2 1/2 pounds sweet potatoes (about 5 medium)
• 2 tablespoons butter, softened
• 1/2 cup firmly packed brown sugar
• 1/2 cup 2% reduced-fat milk
• 1 large egg
• 1/2 teaspoon salt
• 1/2 teaspoon vanilla extract
• Vegetable cooking spray
• 1 1/4 cups cornflakes cereal, crushed
• 1/4 cup chopped pecans
• 1 tablespoon brown sugar
• 1 tablespoon melted butter
• 1 1/4 cups miniature marshmallows