Simple loan with a mortage as collateral
Assuming United States; answer may be different elsewhere. The best instructions I have seen for this were on the webpage of one of the law firms making an organized business out of intra-family loans, but any lawyer who can deal with normal bank loans should be able to help you set this up and get it filed with the appropriate authorities to make it a legally binding mortgage. Shouldn't cost you much in legal time to do it. You will have to charge interest; your lawyer can tell you what the minimum and maximimum interest rates would be where you are. Your interest income will be taxable. The borrower may or may not be able to deduct the interest paid from their taxes. Of course if the borrower has any sense they'll want to get their own lawyer to review the terms of the agreement, and to tell them whether they can deduct it from taxes or not.