In a medium bowl combine OO flour and semolina. On a large clean surface such as a wooden butcher block or cutting board, pour flour mixture into the center. Using the bottom of the bowl create a diviot in the center of the flour to form a round wall.
Carefully add water 1/4 c. at a time and using a fork begin to fold flour mixture inward from the wall to the center. Do this until a tacky shaggy dough forms. Add more water 1 tbsp. at a time if needed. The dough should not be wet or too dry.
Knead dough for about 10 minutes. Wrap in plastic and rest at room temperature for at least 30 minutes.
Remove a small piece of dough and begin by rolling it out into a thin sheet. If you have a pasta maker, you can start on 1 or 2 and work your way to 5 or 6, depending on how thick you want it. Once you've rolled the pasta into a sheet cut it into desired shapes; ie: linguini, pappardelle, bow ties.
Allow pasta to dry on a pasta tree, mesh surface or wooden cutting board covered in semolina. Store in an airtight container on the counter for up to 1 week.