Are peas countable or non-countable?

Frequently in my childhood a conversation would arise at the dinner table that went something like this; "How many peas would you like?" "About sixty please". (Laughter ensues).

The question befits a countable noun such as sausages. However the correct answer is something which befits a non-countable noun such as rice. "Quite a lot", "Not very much", "A spoonful" or "Less" (rather than "Fewer"). Why is it that peas defy classification as countable or non-countable?

I've had it explained to me that the etymology of pea is a back-engineered (and originally incorrect) singular derived from "pease" which would suggest "How much peas would you like?" is a grammatically correct question.

However this doesn't explain why the same problem occurs with other small items such as sliced carrots or cornflakes.

Is it size-related? Is there a no-man's land between rice and sausages where English is simply lacking an appropriate solution?

The question may be "How many peas?" (countable) but the answer is expressed by quantity not count (ie, "A spoonful," as if a mass noun).

Presumably this is because although the items are theoretically countable like apples, they are practically uncountable, like sand.