
Preheat oven to 325° Fahrenheit. Lightly grease 4 8-inch round cake pans with cooking spray or butter. Cut parchment paper circles to fit in bottom of each cake pan - I typically place pan on parchment paper, trace around bottom of pan, then cut along outline.
Prepare white cake mix as directed on box (or according to your cake recipe instructions). Gently stir fresh cranberries into prepared cake batter, then divide batter evenly between cake pans.
Place cake pans in oven and bake at 325°F for 27-30 minutes, or until toothpick inserted in center of cake comes out clean. Be careful not to over-bake cake.
Cover wire cooling rack with sheet of plastic wrap. Flip cooling rack over and place face down on top of cake pan, with plastic wrap covering cake surface. With one hand under cake pan and one hand on top of cooling rack, press the two together and carefully flip them over so cake pan is upside-down on cooling rack. Gently twist and wiggle cake pan while lifting upward to release cake. Repeat for all 4 cakes.
Let cakes cool 5 minutes, then wrap each layer in plastic wrap. Place flat in freezer and freeze at least 8 hours. Note: cakes can be made weeks in advance and frozen until ready to decorate.
Place wire cooling rack face down on top of cake pan. With one hand under cake pan and one hand on top of cooling rack, press the two together and carefully flip them over so cake pan is upside-down on cooling rack. Gently twist and wiggle cake pan while lifting upward to release cake. Repeat for all 4 cakes.
Let cakes rest on cooling racks 2 to 3 hours, until completely cooled. Transfer one cooled cake to plate or cake stand and begin decorating.
In large bowl, use stand mixer or hand mixer to beat softened cream cheese and butter together.
Place white chocolate chips in heatproof bowl and place in microwave (or over double boiler). Microwave in 30 seconds bursts, stirring well between each session. Microwave until just barely melted - if you microwave the chips too much, the chocolate will seize.
Carefully add melted chocolate and vanilla extract to cream cheese mixture and mix well. Gradually add in powdered sugar in several increments, beating frosting mixture until light and fluffy after each addition.
Note: Cake MUST be completely cooled (or completely frozen) before starting this process.Carefully level each layer of cooled cake so they sit flat on top of each other. Keep the layers as evenly thick as possible.
Dollop white chocolate cream cheese frosting in center of one layer of cake - this will be your bottom layer. Use offset spatula to spread frosting out to edges of cake, creating smooth, even layer of frosting.
Take another layer of cake and gently place it on top of frosting layer, centering it so edges line up with bottom layer. Repeat frosting layer and cake layer, alternating each, until all 4 layers have been stacked.
Crumb coat entire outside of cake. To crumb coat, dollop small amount of frosting on center of top layer and spread to edges in very thin layer. You should still see cake through frosting layer. Visible crumbs in frosting layer are normal and fine.
Continue this process down all sides of cake, crumb coating entire exterior in very thin layer of frosting. Be gentle and avoid pushing or pulling on cake surface.
Place crumb coated cake in refrigerator and chill 30 minutes.
Once crumb coat feels set and dry, remove cake from fridge and finish frosting. Dollop frosting on center of top of cake and use offset spatula to gently spread frosting out to edges and down sides of cake, coating cake fully.
Decorate top and sides of cake as desired, with sugared cranberries, rosemary sprigs, gingerbread, or white chocolate. If desired, finish cake with sprinkle of powdered sugar through fine mesh sieve to create "snow".
Serve finished cake as desired.