01 - In a medium saucepan, mix diced strawberries, granulated sugar, and lemon juice, ensuring all fruit is evenly coated.
02 - Place saucepan over medium heat and cook for 5 to 7 minutes, stirring occasionally until strawberries release juices and soften.
03 - In a separate bowl, whisk cornstarch with water until fully smooth and no lumps remain.
04 - Pour cornstarch slurry into saucepan. Stir continuously and cook for an additional 3 to 5 minutes until the filling thickens and takes on a glossy sheen.
05 - Remove saucepan from heat. Stir in vanilla extract, if desired.
06 - Allow filling to cool completely before using in desserts. The mixture will become thicker as it cools.
07 - Transfer cooled filling to an airtight container and refrigerate for up to 5 days.