Makes 3 loaves
Soften the yeast in the water.
Combine the rye flour, molasses, butter and salt. Add the boiling water and blend well. Cool to lukewarm. Add the softened yeast mixture. Gradually stir in the white flour to make a soft dough, mixing well.
Turn onto a floured board and cover with a towel. Let rest 10 minutes on the board. Knead the dough until smooth and satiny, about 10 or 15 minutes. Place it in a greased bowl, turning once to grease both top and bottom. Cover with a thin towel again and put in a warm place to rise until doubled in bulk, about 1½ hours.
Punch down in the bowl, turn and let rise until again doubled in bulk, about 30 minutes.
Turn out on the floured board and divide into 3 portions; shape roughly into loaves. Cover them on the board with the towel and let them rest again for 15 minutes.
Shape the 3 loaves more precisely and put them in greased pans (9×5×3). Cover with the towel and let rise about 1 hour. Brush the loaves lightly with beaten agg and bake 35 to 45 minutes in a preheated 350° oven.