Preheat oven to 350°. For pie, roll pastry dough disk, from center to edge, on a lightly floured piece of parchment into a 13-inch round. Gently roll the pastry around the rolling pin; carefully unroll to place it on a 9-inch pie plate. Ease pastry into pie plate without stretching. Trim pastry ½-inch beyond the edge of the pie plate; fold under pastry even with pie plate edge. Crimp edge by pinching edge of dough at an angle between your thumb and index finger to create a rope-like edge. Lightly cover with plastic wrap; freeze for 15 minutes.

For filling, heat butter in a small saucepan over medium heat for 6 to 8 minutes or until butter is light amber-brown in color, stirring occasionally. Remove from heat; cool slightly.

Whisk eggs in large bowl. Add sweet potato purée, milk, maple syrup, cinnamon, nutmeg, ginger, salt, vanilla, allspice and browned butter; gently whisk just until combined.

Place pastry-lined pie plate in a large rimmed baking pan; pour in filling. Bake for 70 to 80 minutes or until a knife inserted into center comes out clean. Cool completely on a wire rack. Refrigerate until ready to serve.

To serve, let pie stand at room temperature for 15 minutes. Meanwhile, for meringue, combine water, ¼ cup ultrafine sugar, meringue powder, cream of tartar, and maple extract in a large mixing bowl. Beat with an electric mixer on medium for 5 minutes or until soft peaks form (tips curl). Add remaining ½ cup sugar, 1 tablespoon at a time, beating on high until stiff peaks form (tips stand straight).

Spread meringue on top of pie; use the back of a spoon to smooth and form peaks. Using a kitchen torch, toast meringue until golden.