Make a sponge, using the milk, salt, and yeast. When it is full of bubbles, add the butter, sugar, and well-beaten eggs. Stir in enough flour to make a soft dough. Knead it for twenty minutes. Let it rise to double its bulk; then mold it into balls the size of half an egg. Place them rather close together in a baking-tin, and let them rise until very light. When they are ready to go into the oven, brush over the tops with sugar dissolved in milk, and sprinkle the tops with dry sugar. Bake in a hot oven about half an hour. Rusks must be well kneaded and be very light before being baked. A part of the dough set for bread may be made into rusks by adding to it an egg, sugar, and butter.