Preheat the oven to 400°. In a medium roasting pan, toss the potatoes with the olive oil and season with salt and pepper. Roast for about 40 minutes, tossing occasionally, until tender and browned. Let the potatoes cool completely.
In a small bowl, combine the mayonnaise, mustard, dill and garlic. Toss with the potatoes and season with salt and pepper.
The potato salad can be refrigerated for up to 2 hours. Let return to room temperature before serving.