What does cook up a storm mean?

[Aiken]

English Language Tests, Intermediate level

ESL/EFL Test #325 "English Slang Idioms (46)", question 7

"I can't wait to go to Grandma's for dinner! I'm hungry, and that woman can cook up a(n) .........," Kathy said to her sister.

(a) storm
(b) army
(c) buffet
(d) horse

English Language Tests, Intermediate level

ESL/EFL Test #325 "English Slang Idioms (46)", answer 7

"I can't wait to go to Grandma's for dinner! I'm hungry, and that woman can cook up a(n) storm," Kathy said to her sister.

Correct answer: (a) storm
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Dear teachers,

Could you please explain the phrase cook up a storm, does this mean grandma cooks very slow?

Thanks in advance.
Aiken
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Man proposes; God disposes

[Mister Micawber]

No. Cook very well and cook many things.
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Native English teacher at Mister Micawber's