1. Peel sweet potatoes, and cut into 3/4-inch cubes. Peel parsnips, and cut into 1/2-inch slices. Peel beets, and cut into 1/2-inch-thick wedges.
2. Toss parsnips and sweet potatoes with 2 Tbsp. olive oil in a large bowl; place in a single layer in an aluminum foil-lined 15- x 10-inch jelly-roll pan. Season with 1 tsp. salt and 1/2 tsp. pepper. Toss beets with remaining 1 Tbsp. olive oil; arrange beets in a single layer on a second aluminum foil-lined jelly-roll pan. Season with remaining 1/2 tsp. salt and 1/2 tsp. pepper.
3. Bake vegetables at 400° for 20 to 25 minutes or just until tender. Let cool 15 minutes or until completely cool.
4. Arrange curly endive leaves on a serving platter; top with vegetables, and drizzle evenly with Horseradish Vinaigrette.