It is actually grammatically correct to drop the "a" here if you use a cookie monster voice
if you're going for crustulum = cookie, you should probably have it accept 'pastry' and 'biscuit' as well seeing as how those are both about as accurate
This must be the most useful sentence in the entire course. :D (Never mind I've only seen a fraction of it yet.)
If the verb is in the imperative, it doesn't go at the end of the sentence. Is that the case?