Preheat oven to 375°F. Combine 2 cups flour, 1 Tbsp. confectioners' sugar and 1 tsp. salt in a bowl. Cut in 2/3 cup chilled shortening with a pastry blender until mixture resembles sand and pebbles. Add 3 to 4 Tbsp. cold water; mix lightly. Pat into a disk, wrap in plastic and chill for 10 minutes.
Roll out dough on a lightly floured surface; press into a 9-inch pie plate. Pierce crust with a fork in several places. Place foil over crust and fill with dried beans. Bake for 10 minutes. Remove foil and beans; bake for 10 minutes more. Remove crust and let cool. Set oven to 350°F.
Whisk 1 1/2 cups sugar, 3 Tbsp. flour, 2 tsp. lemon zest and 1/4 tsp. nutmeg. Add 6 large eggs; beat until combined. Whisk in 4 Tbsp. melted unsalted butter, 1 tsp. vanilla extract, 1/4 cup fresh lemon juice and 1 1/2 cups buttermilk; pour into crust.
Bake until filling is set but still a little jiggly in center, 25 to 35 minutes.