In a heavy-duty saucepan, combine strawberries, water, granulated sugar, lemon juice, and salt.  Cook strawberry mixture over medium-low heat, stirring constantly. Combine water and cornstarch in a small bowl. Set aside.

When mixture reaches a boil and sugar has dissolved, stir in water and cornstarch.  Stir strawberry mixture constantly until it reaches a thick consistency and deep red color.  The filling will be somewhat translucent and should easily coat the back of a spoon.  Your finger should leave a bare line when pulled through the filling on the spoon.

Pour filling into a bowl to cool completely.  You can also strain the filling through a sieve if you want a smooth filling.  Use as necessary.