In a blender or food processor, blend or process 1 cup of the peaches until smooth (you should have 1/2 cup puree).
In a medium saucepan, stir together sugar, cornstarch, and salt. Add water and puree. Cook and stir until bubbly. Cook and stir 2 minutes more. Stir in butter and almond extract.
Arrange remaining peach slices in baked piecrust. Pour puree mixture evenly over peaches. Cover and chill 4 to 24 hours. Serve with whipped cream, if you like.