In a large mixing bowl, combine the ricotta, eggs, granulated sugar, lemon zest, and grappa. Mix with a wooden spoon until smooth and uniform.

Add the flour, baking powder, and salt. Stir until a soft, slightly sticky dough forms. If it clings to your hands in large wet clumps, add flour one tablespoon at a time until it just holds its shape.

Cover the bowl with a plate or plastic wrap and rest the dough at room temperature for 15 minutes.

Pour the oil into a deep, heavy-bottomed saucepan to a depth of at least 8 cm / 3 inches. Heat over medium heat until the oil reaches 170-175 C / 340-345 F. Check with an instant-read thermometer.

With lightly oiled hands, pinch off pieces of dough and roll them into smooth balls roughly 3 cm / 1.2 inches in diameter. You should get about 30 to 35 balls total.

Gently lower 6 to 8 balls into the hot oil using a slotted spoon. Fry for 3 to 4 minutes, turning occasionally, until deep golden brown on all sides.

Lift the castagnole out with a slotted spoon and drain on a plate lined with paper towels. Check the oil temperature and return it to 170-175 C before frying the next batch.

Repeat until all the dough is fried. Dust generously with powdered sugar just before serving.