In a separate bowl combine semolina and plain flour; mix well. Form a well in the centre of the bowl and add salted water and olive oil. Use either a fork or your hands to combine all the ingredients and form a dough. Continue to knead the dough in the bowl. It should be a little sticky.
Place on a well-floured surface and knead for at least 5 more minutes. Wrap with clingfilm and let it rest at room temperature for 30 minutes.
Slice off a small section of the dough; roll it into a thin cord. Keep the remaining dough covered with clingfilm to prevent it drying out. Slice into 1cm pieces; roll each piece on a gnocchi board or on the back of a fork to form the classic gnocchi shape. You will have to press hard to form the shape since the dough is very pliable.
Cook in boiling salted water. They will rise to the top when ready, about 3 to 4 minutes.