Is the new growth lower down then than the burned parts?

If so, I'd cut it back to healthy growth. I pruned back an established clump just before a hot (for us) stretch of weather one year and mine burned like crazy too after I exposed the protected parts to weather. I pruned again...it recovered just fine.

The burned stuff isn't doing anything any harm....if you are not sure how to trim it, don't. It won't do anything for or against the new leaves.
Linda C