01 - Preheat oven to 400°F. Slice the top from the head of garlic to expose cloves, drizzle with olive oil, wrap in foil, and roast for 30 to 35 minutes until tender and golden.
02 - While garlic roasts, heat a large soup pot over medium heat. Add a splash of olive oil, then sauté onion, celery, and potato for 5 minutes until vegetables begin to soften.
03 - Add green peas, thyme, salt, and pepper. Pour in vegetable broth. Bring mixture to a boil, then reduce heat, cover, and simmer for 15 minutes until vegetables are fully tender.
04 - Squeeze the roasted garlic cloves from their skins and add to the soup base.
05 - Use an immersion blender to purée soup until velvety and smooth, or blend in batches using a countertop blender.
06 - Stir in the heavy cream and warm gently over low heat without boiling. Taste and adjust seasoning with additional salt, pepper, or a squeeze of lemon juice if desired.
07 - Ladle soup into bowls and garnish each serving with chives or parsley.