Heat the olive oil in a large saucepan over moderate heat. Add the garlic and let it sizzle for about 1 minute, then add the leek and celery. Cook, stirring often, until the vegetables soften, about 8 minutes. Do not let them color. Meanwhile, pour the diluted stock into another saucepan and bring to a simmer. Add the cream to the vegetable mixture and bring to a simmer. Add the peas and 3 cups of the simmering stock-water mixture and return to a simmer. Adjust the heat to maintain a gentle simmer and cook until the peas are just tender, about 8 minutes. Add the parsley and thyme and simmer for 1 minute longer, then remove from the heat. Transfer in batches to a blender with the ascorbic acid and puree, adding more of the stock-water mixture as needed to thin the soup to a pleasing consistency. Strain the soup through a sieve placed over a clean saucepan. Reheat the soup slowly, but do not let it boil. Season to taste with salt and pepper. Serve in warmed bowls, garnishing as desired with a drizzle of crème fraīche or Basil Oil, or a sprinkling of chives or Prosciutto Bits. | 
