Instructions

 Roll dough into 12-inch circle on floured counter. Loosely roll dough around rolling pin and gently unroll it onto 9-inch pie plate, letting excess dough hang over edge. Ease dough into plate by gently lifting edge of dough with your hand while pressing into plate bottom with your other hand.
 Trim overhang to ½ inch beyond lip of plate. Tuck overhang under itself; folded edge should be flush with edge of plate. Crimp dough evenly around edge of plate. Wrap dough-lined plate loosely in plastic wrap and refrigerate until firm, about 30 minutes. Adjust oven rack to middle position and heat oven to 350 degrees.
 Line chilled pie shell with double layer of aluminum foil, covering edges to prevent burning, and fill with pie weights. Bake on foil-lined rimmed baking sheet until edges are set and just beginning to turn golden, 25 to 30 minutes, rotating sheet halfway through baking. Remove foil and weights and transfer sheet to wire rack. (Crust must still be warm when filling is added.)
 For the filling Meanwhile, whisk ¼ cup sugar and pectin together in bowl; set aside. Bring 2 pounds (907 grams) gooseberries, lemon zest and juice, salt, and remaining ½ cup sugar to boil in large saucepan over medium-high heat. Off heat, using potato masher, coarsely mash fruit, leaving some berries intact. Return to boil over medium-high heat and cook until slightly thickened, about 20 minutes, stirring often.
Whisk pectin mixture and remaining 8 ounces (227 grams) gooseberries into saucepan. Return to boil and cook for 1 minute, whisking constantly. With pie still on sheet, transfer filling to warm crust, spreading into even layer with rubber spatula. Bake until edge of crust is golden, 20 to 25 minutes.
 For the meringue While pie bakes, bring water and cornstarch to simmer in small saucepan over medium-high heat and cook, whisking occasionally, until thickened and translucent, 1 to 2 minutes. Remove from heat and let cool slightly.
 Using stand mixer fitted with whisk attachment, whip egg whites, vanilla, and cream of tartar on medium-low speed until foamy, about 1 minute. Increase speed to medium-high and beat in sugar, 1 tablespoon at a time, until incorporated and mixture forms soft, billowy mounds. Add cornstarch mixture and elderflower liqueur, if using, 1 tablespoon at a time, and continue to beat to glossy, stiff peaks, 2 to 3 minutes.
 While pie is still hot, use rubber spatula to distribute meringue attractively over top of filling, spreading meri-ngue so it touches crust (this will prevent the meringue from shrinking). (See page 21.) Return pie to oven and bake until meringue is light golden brown, about 20 minutes. Let pie cool on wire rack until filling has set, about 4 hours. Serve.