01 -
Heat olive oil and butter in a large pot over medium heat. Sauté the onion until softened, about 5 minutes.
02 -
Add garlic cloves and cook for 2-3 minutes, stirring frequently.
03 -
Pour in the broth, and add thyme and bay leaves. Bring to a boil, then simmer for 30 minutes.
04 -
Remove thyme sprigs and bay leaves. Season with salt and pepper.
05 -
In a small bowl, whisk together egg yolks and Parmesan cheese. Temper the egg mixture with a ladle of hot soup, then whisk the mixture back into the pot.
06 -
Simmer for 5 more minutes, stirring continuously until the soup thickens. Serve hot with crusty bread and garnish with fresh parsley if desired.