Prepare a 9X13 pan by spreading softened butter all over the bottom and sides of the pan. I like to do this by placing a sandwich bag over my hand like a glove and then using my fingers to spread the butter all around. You can use cooking spray also, but you'll be able to taste it since you don't bake the rice krispie treats and I prefer the taste of butter!
In a large stockpot, melt the butter over medium-low heat. Add 1 1/2 bags of marshmallows and stir over low heat just until barely melted and smooth.
Remove from heat and add the cereal and cranberries. Mix to combine and then add the remaining marshmallows and white chocolate chips. Pour the mixture into the prepared pan and press with your hand until evenly distributed in the pan. (You can use that same sandwich bag that is coated with a little bit of butter to do this if the mixture is sticking to your fingers!)
Let cool for about an hour and then slice and serve. Drizzle with a vanilla glaze if desired.
In a large bowl, mix together the powdered sugar, nutmeg and salt.
In a small bowl, mix the melted butter, milk, cream and vanilla. Make sure to let the butter cool for a few minutes before adding the milk and cream so they don't curdle!
Whisk the butter mixture into the sugar mixture until smooth. If the glaze is too thick, add a little bit more milk, a tablespoon at a time until the glaze reaches your desired consistency.
Pour over cooled rice krispie treats - I like to do this after they are sliced and right before serving. I like to put the glaze in a condiment bottle so that it is easy to squirt out the perfect drizzle. Some people may not want the glaze and you may not want the kids to have the glaze all over their hands!