Mix the oils and lye as you would with any other batch. However
, because you're working with lower temperatures, and a thickened lye solution, I recommend (especially your first few times making soap with milk) that you mix the soap very well - get it to a really thick trace
before you pour it. If you don't, it's possible to get what's called "false trace" - and your soap will separate or develop pockets of lye in it. Get it good and thick!