Put the potatoes in a saucepan and cover them with cold, salted water. Bring the water to a boil, then cook the potatoes for about 10–15 minutes, until fork-tender but still firm enough to hold their shape.

Drain the potatoes well and allow them to cool for several minutes, or use them warm according to your preference. Avoid letting them sit in water after cooking, since excess moisture can make the finished salad watery.

Whisk the olive oil, lemon juice, Dijon mustard, apple cider vinegar, honey or maple syrup, minced garlic, kosher salt, and black pepper together in a small bowl. Continue whisking until the dressing looks blended and lightly thickened.

Place the chopped kale in a large bowl and add a small spoonful of the dressing. Massage the leaves with clean hands for 1–2 minutes, until they become darker, softer, and less bulky.

Add the potatoes, red onion, parsley, and optional feta to the kale. Pour over the remaining dressing and toss gently so the potatoes remain intact.

Let the salad stand for 10–15 minutes before serving. Enjoy it warm, at room temperature, or chilled.