In a bowl, mix water, yeast, oil & salt. Beat in the white flour, followed by the whole wheat flour. Mix well. Oil the dough's surface & allow to proof till light, about 25 minutes. Knead dough slightly, till soft. Cut into 6 pieces & roll each piece in cornmeal. Form each ball into muffins, 10 cm in diameter. Place on a cookie sheet. Preheat oven to 180ºC & bake for 15 minutes.