Cook new potatoes in boiling water to cover in a Dutch oven 20 minutes or until tender; drain and cool slightly. Cut new potatoes in half, and keep warm.
Remove and discard ribs from chard. Rinse chard with cold water; drain and shred.
Cook chard, 1/4 teaspoon salt, and onion flakes in boiling water to cover in Dutch oven 10 minutes; drain and return to Dutch oven. Add potato, and keep warm.
Melt butter in a heavy saucepan over low heat; whisk in flour, and cook, whisking constantly, 1 minute. Gradually whisk in milk; cook over medium heat, whisking constantly, until thickened and bubbly. Stir in remaining 3/4 teaspoon salt and pepper. Pour over vegetables, and toss gently. Serve immediately.
Note: To make ahead of time, spoon creamy mixture into a lightly greased 11- x 7-inch baking dish. Chill until ready to serve. To reheat, bake at 350º for 10 to 15 minutes.