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.

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.

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.

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.

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.

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.

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.

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.

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.

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.