Combine the ricotta, semolina flour and eggs in a mixing bowl and work into a dough. Mix in the Parmigiano-Reggiano, and then the all-purpose flour a little at a time, while kneading the dough into a beautiful, even consistency.
Roll a handful of the dough into an approximately 1-inch-thick log, and then slice into 1-inch pieces to create your ndunderi. Repeat with the remaining dough. Take each piece and lightly press with your thumb, and then roll them down the back of a fork or against a cheese grater to create ridges.
Bring a pot of salted water to a boil, and then add the ndunderi and cook until they rise to the surface, about 3 minutes. Drain well, reserving 4 tablespoons of the cooking liquid.
Add the ndunderi into the sauce with the cooking liquid and cook altogether until the sauce thickens and clings to the ndunderi, about 3 minutes.
Remove from the heat, season with salt and sprinkle with Parmigiano-Reggiano.