In a mixing bowl, pour boiling water over cracked wheat; let stand for 5 minutes. Drain well.
In a large mixing bowl, stir together 1 cup of the bread flour, the yeast, and salt. Add the 1-1/2 cups warm water. Beat with an electric mixer on low speed for 30 seconds, scraping bowl constantly. Beat on high speed for 3 minutes. Using a spoon, stir in the rye flour, cracked wheat, and as much of the remaining bread flour as you can.
Turn dough out onto a lightly floured surface. Knead in enough remaining bread flour to make a moderately stiff dough that is smooth and elastic (6 to 8 minutes total). Shape into a ball. Place in greased bowl; turn once to grease surface. Cover and let rise in a warm place until doubled (about 1 hour).
Punch dough down. Turn out onto lightly floured surface. Divide in half. Cover; let rest 10 minutes. Shape each half of dough into a round loaf. Place on a greased baking sheet; flatten slightly to 5 inches in diameter. With a very sharp knife, make 3 or 4 slashes 1/4 inch deep across top of each loaf. Cover; let rise until nearly doubled (30 to 45 minutes).
Brush tops with a mixture of egg yolk and the 1 tablespoon water.
Bake in a 375 degree F oven about 40 minutes or until bread sounds hollow when you tap the top with your fingers. Cover loosely with foil the last 10 to 20 minutes, if needed, to prevent overbrowning. Remove; cool on wire racks. Makes 2 loaves.