Sliced Sweet Potato Cream Pie

3 or 4  par boiled sweet potatoes  peeled and sliced
1 unbaked deep-dish pie shell (9 inches)
3/4  cup sugar - plus extra
4 Tablespoons self-rising flour
3/4 to 1 cup heavy whipping cream
1/2 stick margarine softened
1 Tablespoon vanilla flavoring

  RETURN
 
Layer part of the sweet potatoes in the pie shell.  Sprinkle 1/4 cup sugar  over the sweet potatoes.  Dot with some of the margarine.  In a bowl, combine 3/4 cup sugar , flour and vanilla; stir in cream until smooth. 
Pour 1/4 of mixture over sliced sweet potatoes.  Repeat with one more layer of sliced sweet potatoes and sprinkle 1/4 cup sugar over sliced sweet potatoes.  Dot with remaining margarine.  Pour remaining whipping cream mixture over sweet potatoes. (May not need all of mixture. )   Use an additional  pie shell to cut in strips for lattice.  Sprinkle lattice with a little sugar.  Bake in preheated 400 degree oven for 40 to 45 minutes.