In a large stockpot, cook the diced bacon over medium heat until crispy, about 5-6 minutes. Remove bacon and set aside, leaving the rendered fat in the pot.

Add diced onions, carrots, and celery to the bacon fat. Sauté for 6-8 minutes until vegetables are softened and onions are translucent. Add minced garlic and cook for 1 minute until fragrant.

Add the brown lentils, bay leaves, salt, black pepper, and thyme to the pot. Pour in 8 cups of water or broth. Bring to a boil, then reduce heat and simmer uncovered for 30 minutes, stirring occasionally.

While the soup simmers, prepare the spätzle dough by whisking together flour, eggs, milk, and a pinch of salt until smooth and slightly elastic. The batter should be thick but pourable.

Bring a separate pot of salted water to boil. Press the spätzle dough through a spätzle maker or colander with large holes directly into the boiling water. Cook for 2-3 minutes until they float to the surface. Remove with a slotted spoon and set aside.

Slice the smoked sausage and add it to the lentil soup along with the cooked spätzle. Simmer for an additional 5 minutes.

Remove bay leaves and stir in the white vinegar. Taste and adjust seasoning with additional salt and pepper if needed.

Ladle into bowls and garnish with the reserved crispy bacon and chopped fresh parsley.