Rub the butter, sugar and eggs together. Add the milk and yeast, and flour enough to make a thick batter. Let this stand in a warm place until light, and then add flour enough to make as thick as for biscuit. Shape, and put in a pan in which they are to be baked, and let them stand two or three hours (three hours unless the weather is very warm). Bake about forty minutes in a moderate oven. It is always best to set the sponge at night, for it will then be ready to bake the following forenoon. If the rusks are wanted warm for tea, the sponge must, of course, be set early in the morning.