Peel the Yukon Gold potatoes and cut them into uniform 1-inch pieces—this ensures even cooking and the right texture for potato salad. Place them in a large pot, cover with cold water by about 2 inches, and bring to a boil over high heat. Cook for 15-18 minutes until the potatoes are fork-tender but still hold their shape; they should break apart easily but not fall apart. Drain well in a colander and spread them on a baking sheet or large plate to cool to room temperature, about 10-15 minutes. I find that cooling them on a sheet helps them cool faster and more evenly than leaving them in a bowl.

While the potatoes cool, whisk together the mayonnaise, Greek yogurt, and mustard in a large mixing bowl until smooth and well combined. Add the cider vinegar, garlic powder, salt, celery seed, and black pepper, stirring until the spices are evenly distributed and no lumps remain. Taste the dressing and adjust seasoning as needed—remember that potatoes are mild, so the dressing should taste slightly bold at this stage. Finely chop the fresh dill and parsley and fold them in, reserving just a small pinch of each for garnish if desired.

Add the cooled potatoes from Step 1 to the dressing bowl, along with the finely diced red onion. Gently fold everything together until the potatoes are evenly coated with the creamy dressing. I like to use a rubber spatula and fold carefully to keep the potatoes intact rather than mashing them. The warm potatoes will absorb the dressing flavors more effectively than cold potatoes, creating a more flavorful final dish.

Transfer the dressed potato salad to a serving bowl or container and refrigerate for at least 2 hours, or up to 24 hours. This resting time allows the flavors to meld and intensify, and gives the dressing time to fully coat each piece of potato. The salad will taste better the next day as the dill and other seasonings continue to develop. Before serving, give it a gentle stir and taste for seasoning, adding a pinch more salt or vinegar if needed.