In a large bowl, combine the semolina and 00 flours and form a well. Add the water and salt to the center of the well. Using a fork, slowly start to incorporate the flour into the water to form a rough dough. Add a teaspoon of water if the dough is too dry or a dusting of flour if it is too wet.
Lightly flour a smooth work surface and pour the dough onto the flour. Knead the dough until it springs back when you press a finger into it, 8 to 10 minutes. Flatten the dough into an even square. Wrap the dough well in plastic wrap and allow to rest for 1 hour.
Cut the dough into 6 pieces. Roll a piece into a 1/3-inch-thick rope. Cut the rope into 1/3-inch pieces. Press one piece of dough firmly with your thumb against a gnocchi board or the back tines of a fork, rolling the dough as you pull it along to create a shell shape. Continue with the remaining dough, dusting the pasta with 00 flour as needed to prevent sticking.