01 - In a medium saucepan, add diced strawberries, granulated sugar, and lemon juice. Gently stir to ensure strawberries are evenly coated.
02 - Set the saucepan over medium heat. Cook, stirring occasionally, for 5 to 7 minutes until strawberries release their juices and begin to soften.
03 - In a small bowl, whisk together cornstarch and water until completely smooth.
04 - Pour the cornstarch slurry into the saucepan. Stir constantly and cook for an additional 3 to 5 minutes until the mixture thickens and becomes glossy.
05 - Remove from heat and stir in vanilla extract, if desired.
06 - Allow the filling to cool completely before using as desired. For best results, store leftover filling in an airtight container in the refrigerator for up to 5 days.