In a saucepan, add sugar and egg nog. Boil for 2 minutes stirring constantly. Remove from heat and stir in marshmallows, cinnamon and nutmeg. Return to stove top and boil for 6 minutes. The mixture will begin to turn brown. Remove from heat and stir in white chocolate chips, vanilla and butter. Stir until chips are completely melted. Pour into prepared pan and smooth evenly across the pan. Let set in the fridge for 30 minutes and cool completely before cutting into squares.