Do this: Rinse the lilac in water and let it dry on paper for a minute. Pick the flowers from the flower stalk. Pour sugar onto a plate and place a piece of baking paper on a tray or cutting board.
Crack an egg and separate the white in a bowl. Add the flowers and make sure the flowers are completely covered.
Pick up a flower with tweezers and dip it in the sugar, pour it over with a spoon so that sugar comes all around. Pick up with tweezers and shake gently to loosen any lumps but not so that it comes off completely. Put on the baking paper, sprinkle a little more sugar so that the whole thing is really covered and leave for at least a day. Shake gently from time to time so that the flowers do not stick to the cardboard or to each other. The candied lilacs should become completely stiff.
This can also be done with other edible flowers. Here are some that are nice to candied with sugar.
Pansies, rose petals, lavender, elderflowers