Cooks a kind of bread in fires, now and again (6)

'cooks' is the definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.

'a kind of bread in fires now and again' is the wordplay.
'a kind of bread' becomes 'rye' (I've seen this in another clue).
'in' means one lot of letters goes inside another.
'now and again' means one should take alternating letters (letters taken on a regular basis).
The alternate letters of 'fires' are 'frs'.
'rye' inserted into 'frs' is 'FRYERS'.

Can you help me to learn more?