To make the roasted garlic dip, slice a thin sliver from the head of garlic, just enough so the cloves are exposed. Drizzle the cloves with olive oil and place the whole bulb on a small piece of aluminum foil and wrap tightly. Place in the preheated oven and roast for 40 minutes, or until the garlic is tender and creamy. Remove from oven and set aside to cool slightly.
Squeeze roasted garlic cloves into a blender or food processor. Add sour cream, Greek yogurt, lemon juice, lemon zest, ground cumin, and cayenne pepper, if using, and blend until smooth and creamy. Season with salt and black pepper, to taste, and transfer to a small serving bowl.