Place 2 lb. small waxy potatoes, scrubbed, in a large pot and pour in water to cover; season generously with kosher salt. Bring to a boil and cook until potatoes are fork-tender, 10–15 minutes. Drain, then let cool slightly (the potatoes should be warm when you dress them).
Step 2
Meanwhile, toast 1 tsp. caraway seeds in a dry medium skillet over medium heat, shaking pan often, until fragrant, about 1 minute. Transfer to a small plate and let cool. Wipe out skillet.
Step 3
Heat ¼ cup extra-virgin olive oil in same skillet over medium-high. Add ½ medium onion, finely chopped, and season with salt and freshly ground pepper. Cook, stirring often, until softened, about 5 minutes. Remove from heat and stir in ¼ cup apple cider vinegar.
Step 4
Transfer potatoes to a medium bowl along with caraway seeds, 4 scallions, thinly sliced, and 2 Tbsp. chopped dill. Scrape oil mixture into bowl; toss to combine, crushing potatoes slightly. Season potato salad with salt and pepper.