I gave two pieces of (cake, cakes) to my parents.

[keannu]

Source : Grammar Zone Basics, 84-C1

Q. Please choose the correct one.
1. I gave two pieces of (cake, cakes) to my parents.

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The answer is "cake", but "cake" is defined as both countable and uncountable nouns in a dictionary.
So can't "cakes" also work here?

 

[GoesStation]

No. Pieces is the plural noun in that sentence; pieces of has to be followed by a singular noun.

 

[probus]

Whether cake is countable or not depends entirely on context.

The countable version of cake normally refers to little individual cakes, those small enough for a single serving. There is obviously little occasion to cut those up. Larger cakes, big enough to be served in slices are usually treated as uncountable. But they too can be countable in the right context. Consider this for example:

So popular were the products of Joe's Bakery that they often ran out of cakes.