Scrub potatoes; leave whole and place in a large pot. Cover with cold water so that there's at least an inch of water above the potatoes. Add 2 tablespoons salt and place over medium-high heat. Bring to a boil, reduce heat to low, and simmer until tender, about 20 to 25 minutes.
Put diced onion and minced garlic in a large bowl with vinegar, remaining salt, and black pepper. Stir to dissolve salt; then whisk in olive oil. Set aside.
When potatoes are done, drain and cut into 1-inch cubes. While potatoes are still warm, toss with onion mixture, mustard, and capers. Add bell pepper, fennel, celery (or lovage), and herbs and toss once more. Serve.
In a “German-style” potato salad like this recipe, you use vinaigrette instead of mayonnaise for the dressing. You may change this recipe to suit your own taste, substituting white onion for red or using a different kind of mustard. Trust your own ideas and get creative, or clean out the fridge! This salad is excellent the next day and up to three days later.