Combine the yeast and the Water in a medium-sized mixing bowl and let stand for 10 minutes, or until dissolved. Stir in the oil and thyme, then the mashed sweet potato, honey, and soymilk. Stir gently until the mixture is smooth.
In another bowl, combine the flours, cornmeal, and salt. Make a well in the center and pour in the wet mixture. Work together, using a spoon at first, then hands, until thoroughly combined into a dough. Turn out onto a floured board and knead for 8 to 10 minutes, adding additional flour until the dough loses its stickiness. Place in a clean bowl and cover with a tea towel. Let rise in a warm place for 1 and 1/2 hours, or until doubled in bulk.
Punch the dough down and turn back out onto the board. Divide into six equal pieces. With hands, roll each piece into a long coil, about 1 inch in diameter. To make each loaf, braid three coils and pinch the ends together.
Place the leaves on a floured baking sheet, cover with the tea towel, and let rise until doubled in bulk, about 1 hour. Brush the tops of the leaves with soymilk. Bake in a preheated 350 degree oven for 40 to 50 minutes, or until the tops are golden and the leaves feel hollow when tapped