In a food processor fitted with the dough blade, combine the yeast, sugar, flour, salt and baking soda.
Combine in a 2-cup measure the hot buttermilk and shortening. With the motor running, slowly pour the liquid through the feed tube. When the dough leaves the side of the bowl and forms a ball (you may not need all the liquid), knead with the machine running for 60 seconds.
Remove the dough and blade from the bowl. Knead the dough by hand for a few seconds, adding flour as necessary if the dough is too sticky. Form dough into a ball. With your thumbs, punch a hole to form a doughnut shape and place into a microwave-safe bowl. Cover with a damp tea towel or microwaveable plastic wrap.
Place an 8-oz glass of water in the middle of the microwave and set the bowl beside it. Heat for 3 minutes at with the power set to 10%. Rest 3 minutes. Heat 3 minutes at 10%. Rest for 6 minutes or until doubled in bulk.
Remove the dough from the bowl, punch down and knead by hand a few seconds. Turn the bowl over top of the dough and let it rest about 10 minutes.
Meanwhile, preheat the oven to 375oF. Grease two glass loaf pans. Cut the dough into 2 pieces. Shape into 2 loaves and place in the prepared pans. Cover the pans loosely with towels.
Replace the pans in the microwave. Place the glass of water in the center and the pans off-center. Heat for 3 minutes at with the power set to 10%. Rest 3 minutes. Heat 3 minutes at 10%. Rest for 6 minutes or until doubled in bulk.
Brush the loaves lightly with egg white and sprinkle with poppy, caraway or sesame seeds if desired. Bake 40-50 minutes, or until loaves are golden brown and tap hollow on the bottom.
I generally make this without microrising the yeast. Each rising takes about an hour to achieve bulk, but the bread comes out a bit lighter.
From the Dinner Co-op