Combine first 5 ingredients in a medium mixing bowl; add pumpkin and butter. Combine egg yolks, milk, and vanilla; add to pumpkin mixture, mixing well. Pour filling into pastry shell. Bake at 350° for 45 minutes or until knife inserted in center comes out clean.
Beat egg whites (at room temperature) until foamy. Gradually add 1/4 cup plus 2 tablespoons sugar, 1 tablespoon at a time, beating until stiff peaks form. Spread meringue over filling, sealing to edge of pastry. Bake at 350° for 12 minutes or until meringue is golden brown. Cool to room temperature before serving.