Sweet Potato Pie

1/4 lb. butter softened
3 mashed sweet potatoes
2 C granulated sugar
1 small can (5 ounces, about 1/2 C plus 2 T) condensed milk
1 t vanilla
3 eggs
2 t cinnamon
1 dash salt
2 prepared pie shells, unbaked

1st - mix mash, yolks and cinnamon
2nd - cream butter sugar and salt
3rd - fold in stiff egg white
4th - 400 degrees F for 10 minutes
5th - 375 degrees F until golden on top