Lentil Soup with Frankfurters

This is Linsensuppe at heart, the thick, tangy German-style lentil soup that pairs earthy lentils with smoky franks. Diced bacon simmers right from the start with leeks, carrots, and celery, building a savory base without any stock or broth needed. Just water, lentils, and time.

The browned flour roux is the technique that makes this soup special. Chopping a whole onion, sautéing it soft, then sprinkling flour over it and stirring constantly until it turns light brown creates a nutty, toasted thickener. That roux gets loosened with a half cup of hot lentil broth and whisked smooth before going back into the pot. It thickens the soup and adds a depth that plain lentils alone don’t deliver.

The splash of vinegar whisked into the roux before it joins the soup is a classic German move. It cuts through the starchiness of the lentils and gives the broth a tangy backbone. Don’t skip it.

Frankfurters and a tablespoon of ketchup go in at the very end, just long enough to heat through. The ketchup adds a subtle sweetness and tomato note that rounds everything out.

Pro Tips

• Brown the flour slowly over low heat and stir without stopping. Burnt flour tastes bitter and will ruin the whole pot.
• Temper the roux by adding hot soup liquid to the pan first, not dumping the roux directly into the pot. This prevents lumps.
• The vinegar should be assertive. White wine vinegar or apple cider vinegar both work. The tanginess fades if you use too little.
• Lentils should be tender but not falling apart. Check at 30 minutes and taste one.

Variations

• Use smoked sausage or kielbasa instead of frankfurters for a richer, smokier soup.
• Add a diced potato for extra body and starch.
• Stir in a tablespoon of whole-grain mustard at the end for a sharper, more traditional German flavor.