How to Make It
To prepare crust, weigh or lightly spoon potato starch and flours into dry measuring cups; level with a knife. Combine potato starch, flours, 1 tablespoon sugar, and salt in a medium bowl; stir with a whisk. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add 3 tablespoons milk; toss with a fork until moist. Gently press mixture into a 4-inch circle on 2 sheets of heavy-duty plastic wrap that overlap; cover with additional overlapping plastic wrap. Chill 1 hour.
Preheat oven to 375°.
Roll dough, still covered, into a 12-inch circle. Fit dough, plastic wrap side up, into a 9-inch pie plate coated with cooking spray. Remove remaining plastic wrap. Press dough against bottom and sides of pan. Fold edges under or flute decoratively. Line bottom of dough with parchment paper; arrange pie weights or dried beans on paper. Bake at 375° for 22 minutes or until edges are lightly browned. Cool completely.
To prepare filling, combine lemon juice and cornstarch, stirring with a whisk. Add egg yolks, stirring with a whisk to combine.
Place 2 cups milk, 2/3 cup sugar, and rind in a large saucepan over medium-low heat, stirring occasionally with a whisk until mixture comes to a boil. Slowly pour one-third of milk mixture into lemon juice mixture, stirring with a whisk. Slowly pour lemon juice mixture into milk mixture, and boil 1 minute or until mixture thickens, stirring constantly with a whisk. Pour into a bowl; add 2 tablespoons butter, stirring until melted. Pour hot filling into cooled crust.
To prepare meringue, place egg whites and cream of tartar in a bowl; beat with a mixer at high speed until soft peaks form. Add 1/4 cup sugar, beating until stiff peaks form. Spread evenly over filling, sealing to edge of crust. Bake at 375° for 10 minutes or until lightly browned on top. Cool 1 hour on a wire rack. Chill overnight.