How to Make It
Heat olive oil in a large Dutch oven over medium-high. Add ground beef, and cook, stirring often, until meat crumbles, about 3 minutes. Stir in onion, celery, and garlic, and cook, stirring often, until beef is no longer pink and vegetables are tender, about 4 minutes. Drain mixture well, and return to Dutch oven.
Stir in chicken broth and potatoes, and bring to boil over medium-high. Cover, reduce to medium-low, and simmer until potatoes are tender, 8 to 10 minutes.
Melt butter in a nonstick skillet over medium-heat. Whisk in flour, and cook, whisking constantly, until flour is lightly browned, about 2 minutes. Stir flour mixture into beef mixture; bring to a boil over medium. Reduce heat to low, and simmer, stirring occasionally, until thickened, about 6 minutes. Stir in cheese, milk, Dijon, salt, and pepper; stir until cheese melts, about 1 minute. Serve soup topped with Sesame Seed Bun Croutons, chopped tomatoes, and chopped pickles.