The tradition of freezing the top tier of your wedding cake is pretty simple. After you and your groom cut the cake and feed each other, the catering staff will bring your cake into the kitchen where they will slice it, plate it and serve it to your guests.
They will remove the top tier and wrap it in plastic wrap, place it in a box that is clearly labeled (and probably supplied by your baker) and then seal the box and wrap the box in plastic wrap too.
Make sure you tell the caterer or location manager who is in charge of taking the cake home for you, especially if you're leaving for your honeymoon right after the wedding.
You should place the cake on a flat surface in your freezer where the box (and the cake) won't got damaged by other items. The day before your first anniversary place the box in the refrigerator to thaw and by the night of your first anniversary it should be ready for you to cut it and feed each other a slice - just like you did at your wedding. You may even want to play the song the band played when you cut the cake at your wedding.
To be honest, I don't care what any baker says, your cake will probably not be as delicious as it was on your wedding day, so here's what I suggest.
On your one month anniversary defrost and enjoy the top tier of your wedding cake and then when it's about a month out from your first wedding anniversary call your baker and ask them if they can make you a replica of the top tier of your wedding cake and pick it up the day of your anniversary. This way you'll be able to enjoy (it's guaranteed to be) a delicious cake.
