Mound semolina and all-purpose flours and salt in 3 separate piles on a large, clean work surface.
Using your fingers, swirl ingredients together until combined.
Gather flour mixture into a pile, and create a well in center. Pour 1/2 cup water into well.
Gradually incorporate flour mixture into water using your fingers.
Once all the water is absorbed, continue adding water, 1 tablespoon at a time, until mixture begins to form a dough.
Start to gather and knead dough, working it until no dry flour remains on work surface.
Continue to knead until smooth and elastic, about 5 minutes.
Divide dough into 16 equal portions, and cover them with a clean, damp kitchen towel.
Roll 1 portion of dough into an 18-inch-long rope.
Use a knife to cut and drag a 1/3-inch piece of dough from end of rope facing you -- a grainy wooden cutting board helps grip the dough.
Holding knife at a 45-degree angle to work surface, press and roll dough toward you.
Unfurl each piece of dough over your thumb in the opposite direction to form a concave shape, and transfer to a rimmed baking sheet lightly sprinkled with semolina flour. Repeat with remaining dough. Orecchiette can be stored at room temperature in a single layer overnight; cover with a clean kitchen towel or plastic wrap.
Any extra orecchiette can be frozen up to six weeks: First, freeze them in a single layer on a baking sheet; then transfer them to a resealable plastic bag, and return them to the freezer. Boil directly from the freezer.