OK so Melba toast is a notorious pain in the bum but my way is so much easier and looks better.
Normally you would toast your bread then cut the crusts off slice it in half so you have 2 really thin slices rub the now untoasted sides on the work surface to smooth it out then grill again! How much hassle is that?
Preheat oven to 100c
Toast your bread
With a rolling pin flatten to your desired thickness
Cut crusts off and cut into triangles
Whack them in the oven until dried out ( about 15 mins ).