1. Let 2 tbsp. of butter come to room temperature. Place garlic, basil, spinach, and parsley in a food processor, and puree. Add butter, mix well, and set aside.
2. Melt the remaining 2 tbsp. of butter in a large, heavy-bottomed pot over medium heat. Add onion and sauté until tender. Add rice and cook, stirring constantly, for about 2 minutes.
3. Bring broth to a simmer in a separate pot. Add hot broth to rice, 1/2 cup at a time, stirring constantly with a wooden spoon, waiting for the liquid to be absorbed before adding more. This will take about 20 minutes, until rice is tender and creamy, not watery.
4. Add the herb puree and parmesan. Season with salt and pepper to taste. Serve immediately in warm bowls.