How to Make It
Preheat the oven to 400°. In a small baking dish, combine the olive oil, thyme sprigs, shallots and garlic. Cover with foil and roast for about 15 minutes, or until the shallots and garlic are very tender. Discard the thyme sprigs. Strain the oil, reserving the shallots and garlic. Let cool.
In a large pot, cover the potatoes with cold water and bring to a boil. Add salt and cook until the potatoes are tender when pierced, about 20 minutes. Drain the potatoes and let them cool slightly, then quarter them and transfer to a large bowl.
Put the reserved shallots and garlic in a blender and puree with the Dijon and whole-grain mustards, the vinegar, lemon juice and cayenne. With the machine on, slowly pour in the reserved olive oil until well blended. Scrape the dressing into a bowl and season with salt and black pepper. Pour the dressing over the potatoes, add the olives and toss well. Sprinkle the chives on top and serve.