This is a hearty, filling, cold-weather soup that makes a meal served with a crusty bread and light salad. The soup is just not the same if the brats are not grilled.
The insistence on grilling the bratwurst is key; it provides a vital smoky depth and char that pan-frying or boiling won't replicate. Achieve good caramelization on your mirepoix (onions, carrots, celery) to build a robust flavor foundation. Fresh herbs like basil and parsley are superior to dried in this soup, adding a vibrant freshness; incorporate them as suggested. For best texture, ensure potatoes are tender but not mushy, and add spinach only at the very end as it wilts quickly. Always taste and adjust seasoning, especially salt, at the final stage, considering the salinity from the broth and brats. A squeeze of lemon juice or a dash of good quality vinegar at the end can brighten the overall profile.