In this sentence:
The insurance premium is small potatoes compared to what we'd have to pay if the house burned down.
"Small potatoes" is a plural noun, but why is the auxiliary verb "is" not "are"?
In this sentence:
The insurance premium is small potatoes compared to what we'd have to pay if the house burned down.
"Small potatoes" is a plural noun, but why is the auxiliary verb "is" not "are"?
If we make 'premium' plural, then we need 'are'.
The insurance premiums are small potatoes compared to what we'd have to pay if the house burned down.
Also we could change things further, e.g.
The insurance premiums are an annoyance compared to what we'd have to pay if the house burned down.
Where there is a discrepancy we decide which is the main subject and make the verb fit that. In your example'small potatoes' describes 'premium' so the latter is the subject of the verb 'to be'.