Janus knows every bakery and confectionery in O'khasis, what deserts they specialize in, and how far they are from the palace (because you know the Lords and Ladies of O'khasis still live in the old Imperial palace from the pre Irene days). He knows exactly which bakery has the best cakes, exactly which places use the freshest ingredients, and exactly what time to get in line to get desserts fresh from the oven.
This isn't for him, it's for Zane.
He does like sweets, but Zane has a serious sweet tooth and coffee hasn't made to Ru'aun yet, so if he wants to have a lot of energy when he's staying up late (or not sleeping at all) he has to eat sugar.
So Janus memorizes all the best places to get his boyfriend sweet things.