Super realtor Kurt Rappaport is selling the most expensive house ever in L.A. ... and it's his!

Real estate sources tell us ... Rappaport is in escrow to sell his incredible 20,000 sq. ft, six-acre Malibu estate for $120 million. We're told it's broken down so that $85 mil is for the home, and $35 mil for the contents of the house. That would make it the most expensive home sold in Malibu or L.A. ... ever. 

We've learned the buyer is Daryl Katz -- the billionaire owner of the Edmonton Oilers hockey team. We're told Katz has been leasing the house for an astounding $750k/MONTH.