Grilled Steak with Rosemary Lemon Butter

lbs beef tenderloin steaks-4 pieces ((otherwise called fillet mignon))

Kosher salt ((or to taste))

coarse ground black pepper

onion powder

dried whole rosemary leaves

olive oil ((if using a stove top grill pan))

Lemon Rosemary Butter:

unsalted room temperature butter

lemon zest

th teaspoon of kosher salt ((or to taste))

th teaspoon of black pepper ((or to taste))

red pepper flakes ((optional but recommended))

chopped fresh rosemary leaves