Steven Tyler & Fiancee -- Big Kahuna Blessed Our Hawaiian Home

Magic conch shells, healing tea leaves ... Steven Tyler and his new fiancee spared no supernatural expense when they blessed their home last week -- and TMZ has learned all the details behind the spiritual experience.

The woman wearing the leaf hat -- or Ley Po'o in Hawaiian -- is Reverand Alalani Hill ... the lead spiritual Kahuna in Maui, who specializes in all sorts of Hawaiian blessings.

Hill tells TMZ, Steven and his fiancee Erin Brady reached out to her recently after buying their house in Hawaii -- and she accepted their invitation, blessing their new home as well as their blossoming relationship.

But it wasn't just a simple blessing -- an elaborate ceremony was involved in the spiritual cleansing process. According to Hill, Steven had to blow on a conch shell (below) to call to the surrounding mountains, ocean, land, and heavens to protect him and his fiancee ... and their new home.

Steven and Erin also had to wear tea leaves and a kukui (indigenous nuts) to represent light and a new beginning, and sing songs to bless the house.