Melt the butter in a cast-iron pan over medium-low heat. Add the thyme and rosemary, and let herbs cook for a minute just until they release their fragrance. Remove from the heat. Allow the thyme and rosemary to infuse in the butter for 20 minutes.
If using a grill, prepare charcoal grill by heating the coals until they’re pale grey and glowing orange, about 20 minutes. Move hot coals to one side of the grill, and place the cast-iron pan with fish on the opposite side.
Eat immediately for that savory taste!