You make two payments per month. One to the lender to repay the interest on the amount borrowed, the other to an insurance company for an endowment contract. There are mainly two types of endowment: unit linked or with profits. Both invest in a broad range of assets including stocks and shares. The capital in the endowment aims to build up over the term of the mortgage to repay the outstanding capital, although to achieve this the investment performance needs to be sufficient to build up the required capital and this performance cannot be guaranteed.