What do mortgage underwriters ask for CPA letters from self-employed borrowers?

• This discussion was modified 11 months ago by  Gustan Cho.

I heard there are non-QM loans for self-employed borrowers that do not require federal income tax returns and no income documentation and is called P and L Statement Non-QM loans. How does the the P and L Statement Mortgage Loan program for self-employed borrowers work? I heard that a CPA Letter is required on a P and L statement non-QM mortgage loan? How does that work?