Cube the potatoes and placed them in a medium sized pot. Cover the potatoes with water, put the lid on the pot and bring the water to a boil. After boiling, cook the potatoes for 4-5 minutes. Check them regularly for your desired doneness. Don't overcook your potatoes -- you're not making mashed potatoes! When done, drain the potatoes in a colander and set aside.
In a small bowl, combine the olive oil, vinegar, spicy brown mustard, sugar, salt and pepper. Use a whisk or fork to combine.
Toss the potatoes and the dressing together in a bowl until all the potato pieces are evenly coated. Serve warm, at room temperature or cold. (You may choose not to use all of the vinaigrette. It's great on salads too!)