Have two 12-cup standard muffin tins ready. Remove the dough from the refrigerator.
Lightly flour a clean work surface. Unwrap the dough, place it on the floured work surface, and flour the top lightly. Roll out the dough into a large circle about 1/8 in/3 mm thick. It will be about 14 in/35.5 cm in diameter. Using a round biscuit or cookie cutter, cut out as many circles 4 to 5 in/10 to 12 cm in diameter as possible.
Handling the dough circles gently, lift each circle and press it into a muffin cup, leaving a 1/8- to 1/4-in/3- to 6-mm overhang and patching any tears by pinching them together or plugging them with a dough scrap. You can crimp the dough that extends beyond the edge of the cup with fork tines or your fingers so it adheres to the top of the tin and forms a rim, if you like, but it is not necessary. Gather the dough scraps, form into a ball, and roll out and cut out more circles. (Reroll the dough only once or it will bake up tough.) You should have 12 to 16 circles total. If you don’t have enough dough circles to fill every cup in a muffin tin, stagger the crusts rather than clustering all of them at one end of the tin. If you’ve filled one tin, refrigerate it while you line the cups in a second tin, then refrigerate the second tin. Refrigerate the lined cups for 30 minutes. Preheat the oven to 400°F/200°C/gas 6.
Remove from the dough-lined cups from the refrigerator. Line each cup with parchment paper, extending it beyond the rim, and fill with pie weights. Place in oven, and bake until the pastry is pale gold, about 10 minutes. Remove from the oven and place on a baking rack. Remove the weights and parchment and let the crusts cool for at least 15 minutes before filling.
In a bowl, whisk together the pumpkin, eggs, brown sugar, milk, sour cream, butter, vanilla, cinnamon, ginger, nutmeg, and salt until smooth. Fill each cooled pastry cup two-thirds full with the pumpkin mixture.
Bake in the oven for 10 minutes. Reduce the oven temperature to 325°F/165°C/gas 3 and continue to bake until the tip of a sharp knife inserted into the center of a pie comes out clean, 12 to 15 minutes longer. The pies are ready if the filling jiggles slightly when a tin is gently shaken.
Let cool completely in the tin(s) on a baking rack, at least 2 hours. The pies should easily lift from the cups when cool. Use a knife tip or fork to pry each pie gently upward so you can grab it with your fingertips and lift it out of the tin. Serve at room temperature.
The pies can be kept in an airtight container at room temperature for up to 2 days or frozen for up to 2 months. Reheat in a 350°F/180°C/gas 4 oven for about 10 minutes.