Line an 8 x 8-iinch pan with parchment paper and coat with cooking spray. Set aside.
In a microwavable bowl, combine the white chocolate, heavy cream, and 5 tablespoons of the sweetened and condensed milk. Set aside.
In a separate microwavable bowl, combine the milk chocolate chips, cinnamon, nutmeg, and the remaining sweetened and condensed milk. Melt this firt by microwaving it for 30 seconds. When you take it out, stir it and make sure all is melted and combined. If not, microwave for another 10 seconds, or until completely melted.
Once the dark mixture is melted, quickly add the vanilla extract and mix it well.
Pour the mixture into the prepared pan and evenly distribute it.
Next, melt the white chocolate mixture using the same method as before. Pour this over the dark layer in the pan, distribute evenly.
Evenly spread the marshmallows on the top layer and gently press them into the mixture.
Refrigergate for 2 hours or until completely set. Once it the fudge has set, use the parchment paper and carefully remove the fudge from the pan. Cut and servie.
Do not microwave either of the mixtures too many times or the chocolate will seize and you won't be able to user it. To avoid this issues, use a double boiler to melt the mixtures.