ペアの単語の微妙なニュアンス
shoe/shoesとかのニュアンスに違いがあるらしい。shoe?と聞くとその靴自体の作りとかスタイルのことを示して、shoesだと大まかな種類のことになるっぽい。
What kind of shoe? asks about the make and style of the particular shoe you have bought
What kind of shoes ? asks about the types of shoes that you have bought.
The same would apply to your example of cake and cakes.
I think the difference is better illustrated if the question is about a car you have bought.
Question:What kind of car did you buy?
Answer: I bought a sports car.
Question: What kind of cars were for sale at the garage?
Anaswer: They sold only very expensive models.
