Thoroughly mix the flour, semolina, and yeast with a couple of generous pinches of salt. Mix 1½ cups warm water with the olive oil. Make a well in the middle of the flour mixture and gradually add the liquid. (It’s easiest to mix this together with a fork to start with and then, when it is just coming together, use your hands to make it into a ball.) Tip the dough out onto a lightly floured surface and knead for about 10 minutes until smooth, elastic, and springy to the touch.