Clean head of cauliflower, then slice it lengthwise through the core into about 4-inch steaks (reserve).
Chop cilantro fine and add all ingredients into food processor and make into a paste. Slowly add olive oil and complete forming the paste. Cut the butter into small cubes and pulse into processor one at a time to form compound butter.
Roll into a 1/2 piece of parchment and into a cylinder and refrigerator.
Pre-heat grill. Brush the steak with a little oil and season with salt and pepper.
Roast on the grill for 4 minutes each side, then place in center of plate and finish with harissa butter.