In a small bowl, use a fork to mix the dried yeast, ¼ teaspoon of the sugar and a tablespoon of warm water. Leave the yeast to activate for about 5 minutes, or until the mixture is foamy.
Mix the semolina, flour, salt and remaining sugar together in a large bowl. Add the olive oil, yoghurt, yeast mixture and 120ml/4fl oz warm water. Use your hands to bring the ingredients together to form a soft dough. The dough should feel slightly sticky. If your dough is too dry, gradually add a little extra warm water, a tablespoon at a time, until you get the right consistency. If it’s too sticky, add a bit more plain flour.
Lightly dust a work surface with semolina and knead the dough for about 10 minutes until smooth and elastic – to check that it has been kneaded enough, press the dough with your finger and it should bounce back, if not keep going for a few more minutes. Divide the dough in half and shape each into a round ball. Cover each loaf with cling film and leave to rest in a warm place for 15 minutes.
Divide the dough into 6 equal balls. Using your hands, flatten each ball into a 6mm/¼in-thick disc and dust both sides with semolina flour. Place the flatbreads on a tray or work surface in a warm place, leaving at least 5cm/2in between each. Cover with cling film and leave to rise for about an hour, or until they double in size – they may need longer if the room is cold.
Lightly oil a frying pan, ideally heavy based, over a medium heat. When hot, place a flatbread in the pan and cook for about 5 minutes on each side, or until golden-brown. Remove from the pan and place on a wire rack while you cook the other flatbreads in the same way. Leave the bread to cool for a few minutes before serving.