Measure the flour, baking powder, and salt onto a large wooden board or onto your counter. Make a well into the center, then measure the ricotta, egg, and milk into the well. Using your hands, start mixing the ingredients together, scooping and squeezing until the ingredients begin to come together into a dough. Knead the dough for about 10 minutes, until it is smooth and you can form it into a large ball. A good sign that the dough is ready is when your hands are clean rather than sticky with wet dough and flour. Cover the dough with a kitchen towel and let it rest for about 10 minutes.
Set a few sheet pans nearby for holding the cavatelli as you shape them later. Line the sheet pans with either kitchen towels or parchment paper, then lightly dust them with flour. Lightly flour your work surface for hand-shaping the cavatelli (or set up your cavatelli maker, if available).
To shape the cavatelli by hand, cut the dough in half and set half of your dough on your lightly floured work surface. Dust the top of the dough with alittle flour. Using a rolling pin, roll the dough into a rectangle about 11 by 12inches and about ¼inch thick. Lightly dust the top with alittle flour to prevent sticking when you shape the cavatelli.
Cut the rolled out dough into ½-inch-wide strips, then cut the strips into ½-inch pieces. Using your index and middle fingers, press your fingers into each piece, gently pushing into the dough while pulling your finger toward you to form a free-form shell. Place the shells on the flour-dusted lined cookie sheets and repeat until you run out of dough.
You can cook the cavatelli right away or freeze them for up to 3 months. To freeze them, place the cookie sheets on a flat shelf in the freezer and leave them for a couple of hours. Turn the frozen cavatelli into bags or other freezer containers (label and date them) and keep them in the freezer for future use.
To cook your cavatelli, bring a covered large pot (an 8-quart pot is perfect) of lightly salted water to a boil over high heat. When the water reaches a boil, carefully add the cavatelli (fresh or frozen) and don’t stir them for about a minute or they’ll stick together. After about a minute, stir the cavatelli. After about 5-8 minutes, you’ll see the cavatelli float to the top. (The exact time will depend on whether they’re fresh or frozen, and how long it takes the water to return to a boil.) Stir the cavatelli again. Taste for doneness. When they are cooked to your preference, drain them into a colander placed in your sink.
Turn the cavatelli into a serving bowl and top with your favorite sauce; toss gently. Serve with grated cheese, such as Pecorino Romano or Parmigiano Reggiano, and freshly cracked black pepper, if desired.