Take a sharp knife and cut the tip of the garlic head off so you slightly expose the cloves inside. Place in a large piece of aluminum foil and drizzle with 2 tablespoons olive oil and ¼ teaspoon salt. Wrap the foil up around the garlic, place it in a baking dish and bake 45 minutes. Cool 10 minutes and then squeeze out the garlic cloves.
In a small bowl, combine the roasted garlic, mayonnaise, sour cream, onion powder, garlic salt, black pepper and dried rosemary. Stir. Cover and refrigerate at least 2 hours, or overnight for best results.
For the potatoes, fill a large pot with water and 1 tablespoon salt. When the water is boiling, add potatoes. Cook 15 minutes or until fork-tender.
Drain and lightly salt the potatoes. Then skewer a green olive and place it on top of the potato. Serve with the garlic dip.
Notes: You can also use microwave-in the-bag potatoes. When serving the dish, you can add plastic eyeballs to the plate to increase the creepy factor.