Combine the wheat flour, besan, semolina with other dry spices. Mix well and add the soda. mix thoroughly. In a separate bowl combine the butter and oil at room temperature. Add this to the flour mixture little by little and crumble well unitl blended. Add water little by little to form this to a firm dough, cover and keep aside for 5-10 minutes. Take a small ball and roll them into thin flat roti. Sprinkle sesame seeds on this and press firmly. Cut them into stripes and then to diamonds again. Deep fry them in hot oil until brown and crisp. If they puff up when frying, mildly press them with the laddle and it will diminish. Drain and store. Alternatively, the calorie conscious can bake these chips on greased baking tray in a pre-heated oven at 175 celcius for 7-8 minutes or till crisp. (spread some oil on the roti before cutting into diamonds for better crispness) Delicious and healthy snack ready