To the bowl of a food processor, add all ingredients and pulse until smooth (scrape down the sides of the bowl to make sure all ingredients are pulsed). The butter will turn a vibrant green. Lay a large piece of plastic wrap on the counter and with a spatula, carefully place an even layer of the mixture down the bottom edge of the plastic wrap, about 1½ to 2 inches in diameter. Fold the bottom edge of the wrap over to cover and seal in the butter. Roll up the plastic wrap like a sausage. Pinch each end and roll the wrapped butter toward you until it’s evenly distributed and the air pockets are gone. Re-wrap with plastic wrap so ends don't come untied. Cool in an ice bath until the butter hardens. Slice off a ½-inch portion and set atop a freshly-grilled steak.