Cook bacon in a large saucepan over medium heat 6 to 7 minutes or until crisp; remove bacon, and drain on paper towels, reserving 1 tsp. drippings in saucepan. Finely chop cooked bacon. Sauté shallots and garlic in hot drippings over medium heat 2 minutes or until tender.
Process 3 cups peas and 3/4 cup reserved cooking liquid in a food processor until smooth. Add pureed pea mixture, remaining peas, salt, and pepper to shallot mixture. Stir in buttermilk. Cook over medium heat, stirring often, 8 minutes. (Do not boil.) Stir in up to 1/4 cup cooking liquid, 1 Tbsp. at a time, until desired consistency is reached. Spoon soup into 4 bowls, and top with bacon.