Mix together semolina, unfed starter and water in a bowl with a fork. Form a ball with your hands. The dough is quite stiff. Turn the ball out onto a generously floured surface and knead for seven minutes until smooth and no longer sticky. Sprinkle on more flour as necessary while you knead.
Let the dough rest for about 20 minutes.
Divide the dough into two equal portions. Roll out the first portion into a rectangle to a thickness of from 1 mm to 1.5 mm. Dust with flour as necessary as you continue to roll out the dough thinner and thinner. You don’t want it sticking to your rolling pin or your work surface.
Dust the rectangle with flour, roll it into a tube slice off noodles. Repeat with the second half of dough.
Cook pasta in salted, boiling water for 1 minute or longer (but not much longer) until tender. These get sticky if you overcook them.