Step 1

Place potatoes in a large pot; cover with cold water by 1 inch and season generously with salt. Bring to a boil; reduce to a simmer and cook until potatoes are tender, about 15 minutes. Run under cold water to cool slightly, then drain.

Step 2

Meanwhile, in a large bowl, whisk together oil, mustard, vinegar, shallot, parsley, and thyme; season with salt and pepper. Add potatoes and onion and toss to combine. Serve at room temperature. To store, refrigerate, up to overnight.