In a large bowl, combine yeast, whole wheat flour, unbleached flour and sugar.
In a saucepan, gently heat the soy milk till lukewarm. Add the cider vinegar. Mixture will curdle slightly. Do not panic.
Slowly add soy milk to the flour. Mix using a food processor or standing mixer, or stir briskly with a large wooden spoon. Pour in warm water and continue mixing until batter is thick. If it feels sticky, work in a few tablespoons more flour. Knead until dough is slightly elastic.
Sprinkle corn meal on a baking sheet. Turn bread dough onto baking sheet and shape into a 7-inch round.
Cover with parchment or a kitchen towel and set aside to rise for 2 hours or until the dough does not spring back when gently poked.
Brush bread with oil and sprinkle sea salt and optional seeds on top. Cover again and let rise for another 2 hours.
Preheat oven to 400 degrees.
Prick the top of the bread lightly with a fork. Place the baking sheet of bread on the middle rack and bake for 15 minutes. Reduce heat to 325 and continue baking for another 25 to 30 minutes, or until loaf is golden and sounds hollow when gently tapped.