Sugared cranberries: Bring 1 cup of sugar and water to a simmer in a saucepan, stirring until sugar is dissolved. Pour syrup into a bowl and cool. Add cranberries and toss until coated. Refrigerate overnight.
Remove cranberries from syrup and roll in remaining 1/2 cup of sugar. Roll several times until well coated. Let dry for several hours.
Cranberry cake: Preheat oven to 350. Line three 8′ cake pans with parchment paper and spray with baking spray and dust with flour.
Combine flour, sugar and baking powder in bowl of electric mixer. Add butter, eggs, vanilla, sour cream and milk and mix on medium spray until smooth. Do not over mix!
Gently stir in cranberries. Spread batter evenly between the cake pans. Bake 35 to 40 minutes or until a toothpick inserted into center comes out with just a few crumbs. Cool on rack.
White chocolate buttercream frosting: Place white chocolate in a metal bowl. Heat whipping cream until simmering and stir into chocolate. Whisk until smooth and let cool completely. It will be thick.
Cake assembly: Cut off domed tops of cake layers if necessary. Place first layer of cake on cake platter. Spread icing on top in an even layer. Add second layer and add more icing on top in an even layer. Add final layer of cake on top and ice the outside of the cake. Top the cake with sugared cranberries and add some around the edges if desired.