In a medium sauepan, stir together sugar, water, salt and cornstarch. Bring to a boil over medium heat, stirring constantly. (This is extremely important). Continue to cook and stir for about 1 minute or until thick and glossy(make sure this is done).
Remove from heat and stir in jell-o and strawberry extract. Let cool to room temperature.
Place 1/2 the sliced strawberries over bottom of baked pie shell. Place 1/2 the filling mixture over strawberries. Use the remaining strawberries except for 2 and cover with remaining filling.
Chill in refrigerator for 2 to 3 hours before serving.
Spread cool whip or whipped topping on the top of the pie and place the 2 reserved sliced strawberries on top.