Linsensuppe Mit Frankfurter (Lentil Soup with Frankfurters)

This German lentil soup is the real deal, the kind that warms you up from the inside on a cold day. Lentils simmer with diced bacon, leek, carrot, and celery until soft, then get thickened with a browned flour roux and finished with sliced frankfurters and a hit of vinegar.

The roux technique is what makes this distinctly German. Chopped onion sautéed in oil gets dusted with flour that you cook slowly, stirring constantly, until it turns a light brown. This browned flour adds a nutty, toasty depth that raw flour roux can’t match. Watch it carefully because burnt flour tastes bitter and ruins the whole pot.

Temper the roux by whisking in half a cup of hot lentil broth before adding it back to the soup. Dumping cold roux into hot soup creates lumps. The gradual tempering ensures a smooth, even thickening.

The vinegar at the end is essential. Just a tablespoon brightens the whole bowl and cuts through the richness of the bacon and frankfurters. Without it, the soup tastes flat.

Chef Tips

• Use quick-cooking lentils and they’ll be tender in 30 to 40 minutes. Standard green lentils may need longer.
• Slice the frankfurters thick and add them at the end just to heat through. Overcooking makes them split and turn rubbery.
• A tablespoon of ketchup sounds odd, but it adds a touch of sweetness and tomato depth that rounds out the flavor.

Variations

• Use smoked sausage (Kielbasa) instead of frankfurters for a smokier, meatier version.
• Add a bay leaf and a pinch of marjoram during the lentil simmer for a more traditional German herb profile.
• Stir in a spoonful of mustard when serving for extra German flavor.