In a small mixing bowl, dissolve yeast in warm milk. Let stand until creamy, about 15 minutes.
Mix the egg, egg yolks, sugar, and salt. In a large mixing bowl, combine the yeast mixture with the egg, egg yolks, sugar, salt and 3 cups of the flour; stir until well combined. Add the remaining flour, 1/2 cup at a time, stirring well after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and supple, about 8 minutes.
Turn out onto a floured bread board, and cut into 2 equal parts. Form into cylindrical loaves; let rest for 20 minutes. Divide each loaf in half and roll into a long rope for braiding. Fasten the 4 ends together. Braid. End by fastening the ends, and turning each end under the loaf. Place on cookie sheet, and cover with a towel until doubled in size, about 40 minutes.
Brush risen loaf with a beaten egg and sprinkle with poppy seeds. Bake at 400 degrees F (200 degrees C) for 15 minutes. Reduce heat to 350 degrees F (175 degrees C) and bake for an additional 45 minutes, or until golden brown.
