Beat egg yolks until thick and lemon colored. Combine 2 cups sugar and flour; gradually add to egg yolks, beating well. Add butter, mixing well. Dissolve soda in buttermilk; add to egg mixture. Stir in lemon juice and 2 teaspoons vanilla. Pour mixture evenly into pastry shells.
Bake at 425° for 10 minutes; reduce temperature to 350°, and bake 40 minutes or until knife inserted in center comes out clean. Remove from oven.
Beat egg whites (at room temperature) until foamy in a large mixing bowl. Gradually add 3/4 cup sugar, beating until stiff peaks form. Beat in 1 teaspoon vanilla. Spread meringue over filling, sealing to edge of pastry. Bake at 350° for 8 minutes or until lightly browned. Cool.