Spray a 9-inch square pan lightly with cooking spray, then line it with a double thickness of foil (this will make it much easier to lift out of the pan later) with ends of foil extending over sides. Spray lightly again and wipe out any excess spray with a paper towel.

Combine sugars, butter, half and half, molasses and spices in heavy 2-½ quart saucepan; bring to full rolling bail, stirring constantly.

Continue boiling 5 minutes over medium heat, stirring continuously. (It's not necessary but for complete accuracy you can use a candy thermometer - temperature should be 234˚F.) Remove from heat, stir in white chocolate chips till melted.

Set aside ¼ cup marshmallow creme in a small bowl. Add remaining marshmallow cream and vanilla to mixture in pot; beat until completely blended. Pour into prepared pan. Dot with reserved marshmallow cream and swirl with a knife. Let cool completely then lift fudge out of pan with foil "handles" and cut into 1-inch squares.