Place garlic in oven safe container. Cover with oil. Roast at 350° until golden brown and soft. Remove garlic from oil. Cool. Save oil for dressing.
In food processor, combine garlic, 1 teaspoon fresh rosemary and 1 tablespoon lemon juice puree. Add oil and vinegar. Puree until creamy in texture. Chill. Toss arugula with dressing. Lightly add ricotta salata cheese and your favorite croutons and serve with soup.