To roast garlic: preheat oven to 400 degrees. Coat a whole head of garlic with olive oil and place on a double layer of foil. Place on the lower rack of the oven and cook until the skin is brown and the garlic is tender (20-40 minutes). Let the garlic cool. With your fingers, gently squeeze the garlic until the cloves pop out of their skin. Any unused garlic can be refrigerated for later use.
In a small bowl, combine the pistachios, garlic and parsley. Reserve at room temperature. In a large saucepan, combine the beef stock and wine. Bring to a simmer over medium heat and cook until reduced to coat the back of a spoon (10-20 minutes). Whisk in the butter and season to taste. Remove pan from heat.
Sprinkle the steaks with a generous amount of freshly ground pepper. In a heavy skillet, heat oil over medium-high heat. Add steaks to skillet and cook to desired doneness. Remove steaks to a platter and tent with foil to keep warm. Return the sauce to a simmer over medium heat. Spoon sauce onto warm serving plates. Place a steak on the sauce and garnish with the roasted garlic mixture, sprinkling a small amount around the edge of the plate. 4 servings.