Preheat oven to 375°.
Place potatoes in a 13 x 9-inch glass or ceramic baking dish, and drizzle with 3 tablespoons water. Cover with foil and bake at 375° for 45 minutes or until tender. Remove the foil, and cool for 15 minutes. Halve potatoes.
Combine olive oil, vinegar, and mustard in a small bowl, stirring with a whisk. Cook bacon in a large nonstick skillet over medium heat until crisp, stirring occasionally. Remove bacon from pan using a slotted spoon, reserving drippings in pan. Increase heat to medium-high. Place potatoes cut sides down in pan; cook for 5 minutes or until golden brown. Place potatoes in a medium bowl.
Remove and discard roots and outer leaves from ramps; rinse and drain ramps. Pat ramps dry. Thinly slice bulb ends and leaves crosswise to measure 1/2 cup. Add the ramps, bacon, and radishes to potatoes. Drizzle dressing over potato mixture, and sprinkle with salt and pepper. Toss.