Baby crackers

From 150 g of flour and 30 g of yeast diluted in milk, prepare the dough and put in a warm place. Add 450g flour, 120g sugar, butter, egg yolks, a pinch of salt and warm milk to the opare. Knead the dough of strong consistency and put in a warm place to increase in volume, then knead again and divide into 3 parts. Form 3 balls from each part, roll each ball into a 4 cm thick formation with a rolling pin, cut into 4X4 cm squares and put again in a warm place to increase in volume. Put the raised squares in a pan greased with butter and bake in a hot oven until dark yellow, 3 beat the egg whites into a strong foam with 30 g of icing sugar, lubricate the cooled squares on all sides with it and place in a warm oven for drying. Then cut the squares into thin slices, put on a metal sheet and again dry the baby crumbs in a warm oven at medium temperature until ruddy.