If you are making homemade butter to freeze from heavy cream you found on sale you will need to really work to ensure all buttermilk is drained from the butter and wrap in waxed paper like store-bought butter.
If you find that you did not thaw the butter in time you can quickly bring frozen butter to a useable temperature by pulling the butter out and placing you the counter under a glass that has been heated with very hot water until steaming.