Prep the bacon and croutons for the toppings: Slice 2 burger buns into crouton-size pieces and allow to dry out while bacon is cooking. Bake bacon slices at 375°F until crisp, about 35-40 minutes. Drain bacon on paper towels, and toss the cubed buns in the rendered bacon fat. Spread croutons on a baking sheet. Season as desired. Bake at 350°F until browned, 18-20 minutes.

In a Dutch oven over medium-high heat, brown the ground beef. Drain the grease. Add the basil, garlic powder, pub burger seasoning, salt and pepper, stir, and remove from the dutch oven into a bowl and set aside. (I used the pan I cooked the bacon in as my "holding" dish. Fewer dirty dishes.)

Melt 2 T. butter in the Dutch oven over medium heat. Add the diced onion and cook, stirring occasionally, for about 20 minutes so the onion begins to brown. Add to your holding dish with the ground beef.

Add the olive oil, butter and cubed baby potatoes to the Dutch oven, cut side down, and brown over medium-high heat stirring as needed. Takes 5-10 minutes. Remove from the pan and add to the holding bowl with the ground beef/onions and set aside.

Sprinkle the flour over the oil/butter left in the Dutch oven. Cook for 3 minutes over medium heat, stirring. Stir in the beef broth. Reduce heat to medium-low, and stir in the ground beef, onions and potatoes. Cover the pot and let cook for 30 minutes. Stir in the milk. Taste for seasoning and adjust per your taste. Continue cooking 20 minutes more.

Reduce heat to low, and gradually stir in the grated cheese. Stir in celery leaves and sour cream. Simmer while cooking the onion rings for the topping. Ladle into soup bowls, add desired toppings, and serve.