"We often eat desserts." "We often eat a dessert after dinner." What are the rules for plural or singular object numbers in a sentence that uses an adverb of frequency? I don't know how to explain this.
well I haven't actually got your question but I have a Rq. you probably should say" We often eat have a dessert after dinner"
Thanks, I made an account now. I was having difficulty thinking of a good example sentence at the time, so I picked one that ended up being a bit unnatural in one form as opposed to another.

You might also say
"She often takes long lunches."
"She often takes a long lunch."

I understand that both are probably fine, but I'm having difficulty explaining to a student why it is the case. I searched through a few of the major English grammar books, but they are mainly tautological in their explanations. I was hoping someone who had more experience teaching English than I do could distill it into a more general trend.