Legal writing samples

I’m wanting to apply to a few local courthouse internships (they are open to undergrad), however they all require Legal Writing samples and i’m unsure where to start on writing one.

I’ve written case briefs for undergrad Legal courses, but never anything likely professional enough for this, nor 5 pages of a single brief.

Are there any recourses on what is best to write or how to go about doing writing samples? Whenever i try to research i just get the types of samples you can do rather than how to go about writing them.

Thanks in advance, any advice appreciated!