This is a recipe for white chocolate chip brownies, written by your mother. Your mother is one of the few people of her generation who aren't ethically opposed to the mixing of white chocolate and dark chocolate.
Odd, isn't it, that that golem would've been carrying around a recipe your mother wrote?
The part in the description about mixing white chocolate and dark chocolate is probably an offhand reference to racial segregation, which was institutionally enforced in the United States until the 1960s. It may also refer to the lingering belief (particularly among older people) that people of different racial or ethnic backgrounds shouldn't intermarry.