For the Crust:

1. Preheat oven to 350°F. Line a 9x13 pan with foil and spray with nonstick spray. Set aside.
2. In a medium bowl, mix together flour and powdered sugar for crust.
3. Cut in butter (I use my hands, you could also use a fork or a food processor) until the mixture forms a dough. Pat dough into prepared pan.
4. Bake crust for about 10 minutes, until puffed and golden around the edges. Let pan cool completely on a wire rack.

For the Filling:

1. In a medium saucepan over medium heat, whisk together sugar, cornstarch and water until smooth. Bring to a boil and whisk for 2 minutes or until thickened.
2. Remove from the heat; stir in strawberry gelatin until dissolved. Refrigerate until thickened and slightly cooled, about 15 minutes.
3. Spread sliced strawberries evenly over crust. Pour gelatin mixture carefully and slowly over the berries, making sure to cover entire surface. Spread gently if necessary.
4. Refrigerate for several hours, until chilled and set.
5. Before serving, remove from pan, peel off foil, and slice into squares. Top with whipped cream if desired.