Melt the brewer's yeast with some lukewarm milk. Mix with some flour and leave in a warm place for 20 minutes. Add the rest of the flour, eggs, butter, sugar, the remaining milk and salt. Allow the dough to rise for about 1 hour. Cut the dough into 50 gr pieces and make rounds with your hands. Cover and leave for about 1 hour. Fry the rounds on both sides in oil (175°). Fill the still warm rounds with jam using a syringe and sprinkle with confectioner's sugar.