In a bowl, combine the eggs, squash, buttermilk, butter and vanilla. Combine the dry ingredients; add to the squash mixture and mix until smooth. Pour into pastry shells. Cover edges loosely with foil.
Bake at 350° for 35 minutes. Remove foil. Bake 25 minutes longer or until a knife inserted in the center comes out clean. Cool on a wire rack. Sprinkle with nutmeg if desired. Store in the refrigerator.