Brown the Beef: Heat a large Dutch oven over medium-high heat. Add the ground beef and cook for 6 to 8 minutes, breaking it into small crumbles, until browned and it reaches 160°F (71°C). Drain excess grease if necessary, leaving about 1 tablespoon in the pot. This step is crucial as it develops the foundational flavor of the soup.

Cook the Vegetables: Add the onion, carrots, and celery. If the pot seems dry, add the olive oil. Cook for 5 to 6 minutes, stirring occasionally, until the vegetables begin to soften. Stir in the garlic and cook for 30 seconds until fragrant. The vegetables should be tender but not fully cooked at this stage, as they will continue to soften during simmering.

Make the Roux: Add the butter and allow it to melt completely. Sprinkle in the flour and stir constantly for 1 to 2 minutes until the flour is fully incorporated and no dry spots remain. This roux will help thicken the soup and create a creamy texture.

Add the Broth: Slowly whisk in the beef broth, scraping the bottom of the pot to loosen any browned bits. The mixture should become smooth with no lumps. This step is important to incorporate all the flavors from the bottom of the pot.

Add the Potatoes: Stir in the potatoes, thyme, parsley, salt, and pepper. Bring the soup to a gentle boil, then reduce the heat to maintain a steady simmer. The potatoes will absorb flavors and help thicken the soup as they cook.

Cook Until Tender: Cover partially and simmer for 15 to 18 minutes, stirring occasionally, until the potatoes are easily pierced with a fork but still hold their shape. This ensures the potatoes are cooked through while maintaining their texture in the soup.

Add the Dairy: Reduce the heat to low: Stir in the milk and heavy cream. Heat gently until steaming, but do not allow the soup to boil after the dairy has been added. This prevents the cream from curdling and keeps the soup smooth.

Melt the Cheese: Add the shredded cheddar one handful at a time, stirring until each addition melts completely before adding more. The soup should become smooth and creamy. This gradual addition helps achieve a uniform texture without clumps of cheese.

Adjust the Consistency: If the soup is thicker than desired, stir in additional warm broth or milk a few tablespoons at a time. If it seems thinner than preferred, simmer gently for several minutes without boiling. Adjusting the consistency ensures the soup meets your preference.

Rest and Serve: Remove the soup from the heat and let it rest for 5 minutes. Taste and adjust the seasoning if needed. Ladle into bowls and garnish with parsley, bacon, and additional cheddar, if desired. Allowing the soup to rest helps the flavors meld together.