Step 1. Remove label from the unopened can of condensed milk.
Step 2. Fill a deep medium saucepan with water. Add unopened can of condensed milk to saucepan. Cover completely with water and simmer uncovered for two hours. Cool fully before opening.
Step 3. Add butter to mixer and mix for 15 minutes until fluffy. Add cold caramel from can and mix with the butter.
Step 4. Spread over tort layers.
Step 5. Cut and serve.