Preheat oven to 400 degrees F.
Combine the milk and lemon juice to create sour milk. Mix the flours, baking soda, and salt in a bowl. Make a well in the middle and stir in the sour milk vigorously to make a thickish dough. Turn dough out onto a floured board and form into a round cake about 2 inches high and 7 inches in diameter.
Warm an 8-inch cast iron skillet or cake pan in the oven for 3 minutes. Take it out, grease and flour it, and place the round dough "cake" in the pan. Using a wet paring knife, make a cross cut on the top of the dough. Cover the pan and bake in the oven for 40 minutes. Remove from the oven and wrap bread in a clean tea towel to cool, 5 to 6 hours. Serve with smoked salmon and cream cheese.
c.1997, M.S. Milliken & S. Feniger, all rights reserved