Begin by preparing the herring. If you're using herring in oil, drain it well and pat dry with paper towels. If it's in a vinegar brine, give it a quick rinse under cold water to remove excess acidity, then pat dry. Cut the herring into bite-sized pieces, which I've found to be the perfect size for melding flavors without overpowering the palate.

Boil the potatoes until just tender, about 15-20 minutes, depending on their size. I've learned that overcooking them makes the salad mushy, so it's best to start checking them a few minutes early. Once done, drain and let them cool before dicing. This cooling period is crucial as it prevents the potatoes from falling apart when mixed with the other ingredients.

In a small bowl, whisk together the sour cream, mayonnaise, white wine vinegar, mustard, and sugar until smooth. This dressing is the heart of the salad, and getting it right is key. The first time I made it, I used too much vinegar, which overwhelmed the delicate herring. Now, I've found the perfect ratio that complements the fish beautifully.

Add the finely chopped red onion to the dressing. I've discovered that letting the onion marinate in the dressing for a few minutes before combining it with the other ingredients mellows its sharpness and infuses the dressing with a subtle flavor that's just divine.

In a large mixing bowl, combine the diced potatoes, apples, pickles, and chopped dill. The apples add a fresh crunch and a hint of sweetness that balances the savory notes of the herring and pickles. I remember the first time I skipped the apples, and the salad felt like it was missing a crucial element.

Gently fold in the herring pieces, taking care not to break them up too much. The integrity of the herring is important for texture and presentation. I've found that a light hand at this stage makes all the difference.

Pour the dressing over the salad and mix gently until everything is evenly coated. Season with salt and freshly ground black pepper to taste. It's important to season at the end, as the herring and pickles already bring their own saltiness to the dish.

Cover and refrigerate the salad for at least an hour before serving. This resting period allows the flavors to meld together and the dressing to fully permeate the ingredients. I've served it immediately before, and while it was good, the difference in depth of flavor after chilling is remarkable.

When ready to serve, give the salad a gentle stir and garnish with additional fresh dill. The vibrant green of the dill not only adds a pop of color but also a fresh, herby aroma that's incredibly inviting.