In a large Dutch oven, melt butter over medium-high heat. Add celery, onion, and garlic, and cook until tender, about 5 minutes. Add sirloin, and cook until meat is browned and vegetables are tender, about 10 minutes.
In a small bowl, whisk together 1 cup water and flour until smooth.
To pan, stir in flour mixture, broth, bay leaves, tomato purée, Worcestershire, thyme, salt, hot sauce, and pepper. Bring to a boil, and reduce heat to medium-low; simmer, uncovered, for 1 hour, stirring occasionally.
Add lemon juice and cook for 30 minutes, stirring occasionally. Discard bay leaves. Stir in eggs, sherry, and parsley. Garnish with lemon slices and thyme, if desired. Serve immediately.
Notes
Instead of stirring into the pot, sherry can be served on the side and poured over soup as desired. Just divide the ½ cup among small glasses for each guest.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/mock-turtle-soup/