Preheat oven to 425°. Grease a large baking sheet. In a large bowl, stir the flour, cornmeal, baking powder and salt. Add the shortening and butter and blend with your fingers until the mixture resembles coarse meal. Mix in the cheese.In a medium-size bowl, blend ½ cup of the milk with the egg white; add to the flour mixture and stir until combined enough to gather into a ball, adding more of the milk if needed. Lightly knead the dough on a floured surface, then pat or roll it into a 9" round ½" thick. Place the dough on the baking sheet. Brush the top with water and sprinkle with the sesame seeds. Cut it into 8 wedges and bake for 15 to 18 minutes or until golden brown.