spread bacon pieces out so they cover the bottom of an enameled cast iron dutch oven. fry the bacon on medium heat until the bottom of the pan turns a medium brown from the gradoux of the bacon. remove bacon to drain and remove approximately half of the rendered fat. reserve a bit of crumbled bacon to garnish the soup for serving.
sauté yellow onion, green onions, garlic, and fresno (or cayenne) pepper in rendered bacon fat and butter. reserve about 1 tsp. of green onions per serving for garnish. stir occasionally and scrape all of the gradoux from the bottom of pan until veggies are wilted.
add turnips, salt, and black pepper to vegetable mixture. stir well and sauté for 10 minutes. stir occasionally to ensure nothing is sticking to the bottom of your dutch oven.
add bay leaves, thyme, and water. bring to a boil for 5-10 minutes.
cover and cook on low-medium for about 20 minutes or until turnips are tender.
let cool to a safe temperature, remove bay leaves, and use an immersion blender to purée soup.
reheat soup to a hot, serving temperature. add and stir in champagne vinegar immediately before serving.
top with croutons, bacon crumbles, turnip slices, and green onions to serve.