Mix corn starch and sugar in a medium saucepan.
Slice and mash about 1 cup of berries (You will need more than 1 cup of berries to make a cup of mashed berries. I usually start with a cup of whole berries and then add as needed to make a cup of mashed berries.) Add 1/4 cup water to the mashed berries.
Add the mashed berries to sugar and corn starch and cook until the mixture starts to thicken, about 10 to 12 minutes. Add lemon juice and continue to cook to thicken, about another 5 minutes.
Place remaining strawberries in the pie shell. If they’re small, put them in whole; if they’re large slice them.
Pour the cooked berry mixture over the uncooked berries.
Refrigerate at least two hours.
Serve pie with whipped cream.