Note: We brown the meringue topping with a blowtorch. It's a simple process, using a backward-forward motion a few inches above the pie. We recognize, however, that not all home cooks have this tool -- so either broil or bake the meringue until the top is golden brown. If you do have a blowtorch, by all means use it, and note that the meringue will set best if it is added while the lemon filling is still hot.
Remove the dough from the refrigerator and on a lightly floured surface, roll out to a 12-inch circle. Transfer the dough to a 9-inch pie pan, pressing gently to fit, trim the edge to within 1/2-inch of the pan, turn under, and crimp decoratively. Refrigerate for 30 minutes to 1 hour.
Preheat the oven to 375 degrees F.
Line the pie shell with parchment paper and fill with pie weights, dry beans, or rice. Bake until the crust is set, about 12 minutes. Remove the parchment paper and weights and bake until lightly colored, 8 to 10 minutes. Cool on a wire rack before filling. Combine the granulated sugar, cornstarch, milk, water, and pinch of the salt in a large, non-reactive saucepan, whisk to combine, and bring to a simmer over medium heat, whisking occasionally. As the mixture reaches a simmer and begins to thicken and turn clear, 4 to 5 minutes, whisk in the egg yolks, 2 at a time. Slowly add the lemon juice, whisking constantly, and add the zest and limoncello. Add the butter, 1 piece at a time, and whisking constantly, return to a simmer. Remove from the heat and pour immediately into the prepared pie crust.
Beat the egg whites, cream of tartar, and remaining pinch salt in a large bowl with an electric mixer until soft peaks form. Beating constantly, gradually add the confectioners' sugar and beat until glossy stiff peaks form, being careful not to over beat, as this will make the meringue difficult to spread.
Transfer the meringue to a pastry bag fitted with a medium star tip. Working 1 row at a time, pipe the meringue across the top of the hot lemon filling in a zigzag pattern, alternating direction with each row. Cover the pie filling completely, going out to the pastry edges, so the meringue does not draw up or weep during baking. (Alternatively, spread the meringue evenly over the pie filling using a rubber spatula, smoothing out to the pastry edges. Make decorative peaks in the meringue using a dull knife or the back of a spoon.)
To quickly cook the meringue, preheat the broiler with the rack in the highest position. Place the pie under the broiler and cook until the meringue is set and golden brown, 1 to 2 minutes, watching carefully to avoid burning. (Alternatively, the meringue can be cooked in a preheated 325 degree F oven until set and golden brown, 14 to 16 minutes.)
Transfer the pie to a wire rack to cool completely before serving.
Sweet Pie Crust:
Yield:enough dough for 1 (9 or 10-inch) crust
Sift the flour, sugar, and salt into a large bowl. With your fingers, work the butter and shortening into the dry ingredients until the mixture resembles coarse crumbs. Add 3 tablespoons of the ice water and work with your fingers just until the dough comes together, adding more water as needed, 1 teaspoon at a time, to make a smooth dough, being careful not to overwork the dough.
Form the dough into a disk shape, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes before using.